論文リスト

@article{Oudah2019,

title = {Evolution of Superconductivity with Sr-Deficiency in Antiperovskite Oxide Sr_{3−x}SnO},

author = {M Oudah and J N Hausmann and S Kitao and A Ikeda and S Yonezawa and M Seto and Y Maeno},

doi = {10.1038/s41598-018-38403-8},

year  = {2019},

date = {2019-02-12},

journal = {Scientific Reports},

volume = {9},

number = {1},

pages = {1831},

abstract = {Bulk superconductivity was recently reported in the antiperovskite oxide Sr 3−x SnO, with a possibility of hosting topological superconductivity. We investigated the evolution of superconducting properties such as the transition temperature T c and the size of the diamagnetic signal, as well as normal-state electronic and crystalline properties, with varying the nominal Sr deficiency x 0 . Polycrystalline Sr 3−x SnO was obtained up to x 0 = 0:6 with a small amount of SrO impurities. The amount of impurities increases for x 0 > 0.6, suggesting phase instability for high deficiency. Mössbauer spectroscopy reveals an unusual Sn 4− ionic state in both stoichiometric and deficient samples. By objectively analyzing superconducting diamagnetism data obtained from a large number of samples, we conclude that the optimal x 0 lies in the range 0.5 < x 0 < 0.6. In all superconducting samples, two superconducting phases appear concurrently that originate from Sr 3−x SnO but with varying intensities. These results clarify the Sr deficiency dependence of the normal and superconducting properties of the antiperovskite oxide Sr 3−x SnO will ignite future work on this class of materials. © 2019, The Author(s).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akebi2019,

title = {Low-energy electron-mode couplings in the surface bands of Sr_{2}RuO_{4} revealed by laser-based angle-resolved photoemission spectroscopy},

author = {S Akebi and T Kondo and M Nakayama and K Kuroda and S Kunisada and H Taniguchi and Y Maeno and S Shin},

doi = {10.1103/PhysRevB.99.081108},

year  = {2019},

date = {2019-02-07},

journal = {Physical Review B},

volume = {99},

number = {8},

abstract = {We use angle-resolved photoemission spectroscopy with a 7-eV laser, which is capable of ultrahigh energy and momentum resolutions, and investigate bosonic mode couplings in the surface bands of Sr2RuO4. Significantly, our measurements reveal pronounced kink structures at very low binding energies (∼8 and ∼15 meV), which have a strong variation in the renormalization strength among multiple bands derived from the Ru4d orbitals. Neutron scattering has observed phonon modes with the lowest energy scale around 15 meV, which thus could be the main source for the ∼15-meV kink. In contrast, the significant coupling at the lower energy (∼8 meV) is attributed to magnetic excitations, which are reported to be peaked in density of states around 10 meV. The ∼8-meV kink is found to be strongest in the two-dimensional 4dxy-derived band, implying its mechanism to be the electron coupling to ferromagnetic spin fluctuations. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Steffens2019,

title = {Spin Fluctuations in Sr_{2}RuO_{4} from Polarized Neutron Scattering: Implications for Superconductivity},

author = {P Steffens and Y Sidis and J Kulda and Z Q Mao and Y Maeno and I I Mazin and M Braden},

doi = {10.1103/PhysRevLett.122.047004},

year  = {2019},

date = {2019-02-01},

journal = {Physical Review Letters},

volume = {122},

number = {4},

abstract = {Triplet pairing in Sr2RuO4 was initially suggested based on the hypothesis of strong ferromagnetic spin fluctuations. Using polarized inelastic neutron scattering, we accurately determine the full spectrum of spin fluctuations in Sr2RuO4. Besides the well-studied incommensurate magnetic fluctuations, we do find a sizable quasiferromagnetic signal, quantitatively consistent with all macroscopic and microscopic probes. We use this result to address the possibility of magnetically driven triplet superconductivity in Sr2RuO4. We conclude that, even though the quasiferromagnetic signal is stronger and sharper than previously anticipated, spin fluctuations alone are not enough to generate a triplet state strengthening the need for additional interactions or an alternative pairing scenario. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Aoki2019,

title = {Review of U-based ferromagnetic superconductors: Comparison between UGE_{2}, URHGE, and UCOGE},

author = {D Aoki and K Ishida and J Flouquet},

doi = {10.7566/JPSJ.88.022001},

year  = {2019},

date = {2019-01-29},

journal = {Journal of the Physical Society of Japan},

volume = {88},

number = {2},

abstract = {The discovery in 2000 that the ferromagnetic (FM) compound UGe2 (TCurie = 52 K at ambient pressure) becomes superconducting under a pressure of P = 1.1 GPa until it enters the paramagnetic (PM) phase above Pc = 1.6 GPa was a surprise, despite the fact that such a possibility was emphasized in theory four decades ago. Successive searches for new materials (URhGe and UCoGe) led to the discovery of the coexistence of superconductivity (SC) and ferromagnetism at ambient pressure. Furthermore in UCoGe, it was found that SC survives in the PM regime from Pc = 1.1 to 4 GPa. The novelty is that SC also emerges deep inside the FM regime but with strong FM fluctuations. Focus has been on low-temperature experiments under extreme conditions of magnetic field (H), pressure, and uniaxial stress. NQR and NMR experiments are unique tools to understand the interplay between the spin dynamics and the Cooper pairing. We choose to present the SC properties from the knowledge of quasiparticle dressing in the normal phase (renormalized band mass, mB plus the extra dressing originating from FM fluctuations, m++). In UGe2, strong interplay exists between Fermi surface (FS) reconstructions in the cascade of different FM and PM ground states and their magnetic fluctuations. Similar phenomena occur in URhGe and UCoGe but, at first glance, the SC seems to be driven by the FM fluctuations. The weakness of the FM interaction in these two compounds gives the opportunity to observe singular features in magnetic field scans depending on their field orientation with respect to the FM sublattice magnetization (M0). We will show that for UCoGe, which has the smallest ordered moment, a longitudinal field scan (H ∥ M0) leads to a drastic decrease in the FM fluctuations with direct consequences on SC properties such as the upward curvature of the upper critical field. A transverse field scan (H M0) leads to suppression of the Curie temperature, TCurie; the consequence is a boost in FM fluctuations, which leads to a reinforcement of SC. Contrary to the two examples of Ising FM UGe2 and UCoGe, the singularity in URhGe is the weakness of the magnetocrystalline term between the choice of ferromagnetism along the c- or b-axis; the most noteworthy feature is the detection of reentrant SC on each side of the H switch at HR from the c easy axis of magnetization to the b-axis. All the experimental results give evidence that the SC in these three materials originates from the FM fluctuations, which are amplitude modes of magnetic excitations in the FM state. Spin-triplet pairing has been anticipated in the FM superconductors and was actually observed by Knight-shift measurements in the SC state of UCoGe. Their fascinating ð P; T; H Þ phase diagrams are now well established. Of course, a new generation of experiments will elucidate subtle effects by obtaining their SC order parameters. While the FSs of UGe2 have been experimentally well determined, those of URhGe and UCoGe have been poorly determined, and thus a quantitative comparison with band structure calculations cannot be achieved. Up to now, Angle-resolved photoemission spectroscopy (ARPES) measurements have only given the flavor of the electronic bands at the Fermi level. Discussion is presented on how different theoretical approaches can describe the various phenomena discovered by experimentalists. Following the new hot subject of topological superconductors, proposals have been made for UCoGe, which is a great challenge for ambitious researchers!. © 2019 The Physical Society of Japan},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Manago2019b,

title = {Enhancement of superconductivity by pressure-induced critical ferromagnetic fluctuations in UCoGe},

author = {M Manago and S Kitagawa and K Ishida and K Deguchi and N K Sato and T Yamamura},

doi = {10.1103/PhysRevB.99.020506},

year  = {2019},

date = {2019-01-24},

journal = {Physical Review B},

volume = {99},

number = {2},

abstract = {A Co59 nuclear quadrupole resonance (NQR) was performed on a single-crystalline ferromagnetic (FM) superconductor UCoGe under pressure. The FM phase vanished at a critical pressure Pc, and the NQR spectrum just below Pc showed phase separation of the FM and paramagnetic (PM) phases below Curie temperature TCurie, suggesting first-order FM quantum phase transition (QPT). We found that the internal field was absent above Pc, but the superconductivity is almost unchanged. This result suggests the existence of the nonunitary to unitary transition of the superconductivity around Pc. Nuclear spin-lattice relaxation rate 1/T1 showed the FM critical fluctuations around Pc, which persist above Pc and are clearly related to superconductivity in the PM phase. This FM QPT is understood to be a weak first order with critical fluctuations. 1/T1 sharply decreased in the superconducting (SC) state above Pc with a single component, in contrast to the two-component 1/T1 in the FM SC state, indicating that the inhomogeneous SC state is a characteristic feature of the FM SC state in UCoGe. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kostylev2019,

title = {Piezoelectric-based uniaxial strain cell with high strain throughput and homogeneity},

author = {I Kostylev and S Yonezawa and Y Maeno},

doi = {10.1063/1.5063729},

year  = {2019},

date = {2019-01-16},

journal = {Journal of Applied Physics},

volume = {125},

number = {8},

abstract = {We seek for novel electronic phenomena by using external strain engineering, namely, by the application of external uniaxial strain. A piezoelectric-based uniaxial strain cell has been recently developed by Hicks et al. and successfully utilized for studies of various unconventional superconductors. Here, we propose a modified design that minimizes effects originating from the asymmetry of the strain cell design, in particular with minimal bending moments, by placing the sample at the axis of mirror symmetry of the device to balance out the reactive forces. Results of finite element analyses indicate that placing the sample offset to the axis of the mirror symmetry indeed causes an increase of strain inhomogeneity up to 10%, both at room temperature and at 4.2 K. Furthermore, we found that this bending reduces the overall achievable strain down to 30% of its maximal value without the bending. We also experimentally demonstrate the potential of our constructed device by tracking the displacement of the anvils of the strain cell with a parallel plate capacitor. The full range of motion of the piezo-stacks were demonstrated at room temperature. With a sample and at 0.9 K, we achieved a uniaxial strain of - 1.5%, which is enough to induce electronic change in typical materials. © 2019 Author(s).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitagawa2018,

title = {Normal-state properties of the antiperovskite oxide Sr3-xSnO revealed by Sn 119 -NMR},

author = {S Kitagawa and K Ishida and M Oudah and J N Hausmann and A Ikeda and S Yonezawa and Y Maeno},

url = {http://hdl.handle.net/2433/235675

https://arxiv.org/abs/1809.09275},

doi = {10.1103/PhysRevB.98.100503},

year  = {2018},

date = {2018-09-21},

journal = {Physical Review B},

volume = {98},

number = {10},

pages = {100503(R)},

abstract = {We have performed Sn119-NMR measurements on the antiperovskite oxide superconductor Sr3-xSnO to investigate how its normal state changes with the Sr deficiency. A two-peak structure was observed in the NMR spectra of all the measured samples. This suggests that the phase separation tends to occur between the nearly stoichiometric and heavily Sr-deficient Sr3-xSnO phases. The measurement of the nuclear spin-lattice relaxation rate 1/T1 indicates that the Sr-deficient phase shows a conventional metallic behavior due to the heavy hole doping. In contrast, the nearly stoichiometric phase exhibits unusual temperature dependence of 1/T1, attributable to the presence of a Dirac-electron band. © 2018 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ikeda2018752,

title = {Theoretical band structure of the superconducting antiperovskite oxide Sr3−xSnO},

author = {A Ikeda and T Fukumoto and M Oudah and J N Hausmann and S Yonezawa and S Kobayashi and M Sato and C Tassel and F Takeiri and H Takatsu and H Kageyama and Y Maeno},

url = {http://hdl.handle.net/2433/250419},

doi = {10.1016/j.physb.2017.10.089},

year  = {2018},

date = {2018-05-01},

journal = {Physica B: Condensed Matter},

volume = {536},

pages = {752-756},

abstract = {In order to investigate the position of the strontium deficiency in superconductive Sr3−xSnO, we synthesized and measured X-ray-diffraction patterns of Sr3−xSnO (x∼0.5). Because no clear peaks originating from superstructures were observed, strontium deficiency is most likely to be randomly distributed. We also performed first-principles band-structure calculations on Sr3−xSnO (x=0, 0.5) using two methods: full-potential linearized-augmented plane-wave plus local orbitals method and the Korringa-Kohn-Rostoker Green function method combined with the coherent potential approximation. We revealed that the Fermi energy of Sr3−xSnO in case of x∼0.5 is about 0.8 eV below the original Fermi energy of the stoichiometric Sr3SnO, where the mixing of the valence p and conduction d orbitals are considered to be small. © 2017 Elsevier B.V.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hausmann2018,

title = {Controlled synthesis of the antiperovskite oxide superconductor Sr3-xSnO},

author = {J N Hausmann and M Oudah and A Ikeda and S Yonezawa and Y Maeno},

url = {https://arxiv.org/abs/1712.09484},

doi = {10.1088/1361-6668/aab6c2},

year  = {2018},

date = {2018-04-11},

journal = {Superconductor Science and Technology},

volume = {31},

number = {5},

pages = {055012},

abstract = {A large variety of perovskite oxide superconductors are known, including some of the most prominent high-temperature and unconventional superconductors. However, superconductivity among the oxidation state inverted material class, the antiperovskite oxides, was recently reported for the first time. In this superconductor, Sr3-xSnO, the unconventional ionic state Sn4- is realized and possible unconventional superconductivity due to a band inversion has been discussed. Here, we discuss an improved facile synthesis method, making it possible to control the strontium deficiency in Sr3-xSnO. Additionally, a synthesis method above the melting point of Sr3SnO is presented. We show temperature dependence of magnetization and electrical resistivity for superconducting strontium deficient Sr3-xSnO (T c ∼ 5 K) and for Sr3SnO without a superconducting transition in alternating current susceptibility down to 0.15 K. Further, we reveal a significant effect of strontium raw material purity on the superconductivity and achieve substantially increased M/M Meissner (∼1) compared to the highest value reported so far. More detailed characterizations utilizing powder x-ray diffraction and energy-dispersive x-ray spectroscopy show that a minor cubic phase, previously suggested to be another Sr3-xSnO phase with a slightly larger lattice parameter, is SrO. The improved characterization and controlled synthesis reported herein enable detailed investigations on the superconducting nature and its dependency on the strontium deficiency in Sr3-xSnO. © 2018 IOP Publishing Ltd.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bakurskiy2018,

title = {Local impedance on a rough surface of a chiral p -wave superconductor},

author = {S V Bakurskiy and Ya.V. Fominov and A F Shevchun and Y Asano and Y Tanaka and M.Yu. Kupriyanov and A A Golubov and M R Trunin and H Kashiwaya and S Kashiwaya and Y Maeno},

doi = {10.1103/PhysRevB.98.134508},

year  = {2018},

date = {2018-01-01},

journal = {Physical Review B},

volume = {98},

number = {13},

abstract = {We develop a self-consistent approach for calculating the local impedance at a rough surface of a chiral p-wave superconductor. Using the quasiclassical Eilenberger-Larkin-Ovchinnikov formalism, we numerically find the pair potential, pairing functions, and the surface density of states taking into account diffusive electronic scattering at the surface. The obtained solutions are then employed for studying the local complex conductivity and surface impedance in the broad range of microwave frequencies (ranging from subgap to above-gap values). We identify anomalous features of the surface impedance caused by generation of odd-frequency superconductivity at the surface. The results are compared with experimental data for Sr2RuO4 and provide a microscopic explanation of the phenomenological two-fluid model suggested earlier to explain anomalous features of the microwave response in this material. © 2018 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lee2018,

title = {Abnormal phase flip in the coherent phonon oscillations of Ca2RuO4},

author = {M -C Lee and C H Kim and I Kwak and J Kim and S Yoon and B C Park and B Lee and F Nakamura and C Sow and Y Maeno and T W Noh and K W Kim},

doi = {10.1103/PhysRevB.98.161115},

year  = {2018},

date = {2018-01-01},

journal = {Physical Review B},

volume = {98},

number = {16},

abstract = {We employ an optical pump-probe technique to study coherent phonon oscillations in Ca2RuO4. We find that oscillation amplitude of an Ag symmetric phonon mode is strongly suppressed at 260 K, a putative transition point of orbital ordering. The oscillation also shows a gradual but huge change in its phase, such that the oscillation even flips over with a 180 change across the temperature. Density functional theory calculations indicate that the Ag phonon has an eigenmode of octahedral distortion with conventional tilting along the a axis and antipolar distortion of apical oxygen. Careful inspection of the lattice captures an unusually large antipolar distortion in low-temperature structures, which may play a crucial role for the phase transition at 260 K. © 2018 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{OldeOlthof2018,

title = {Theory of tunneling spectroscopy of normal metal/ferromagnet/spin-triplet superconductor junctions},

author = {L A B Olde Olthof and S -I Suzuki and A A Golubov and M Kunieda and S Yonezawa and Y Maeno and Y Tanaka},

doi = {10.1103/PhysRevB.98.014508},

year  = {2018},

date = {2018-01-01},

journal = {Physical Review B},

volume = {98},

number = {1},

abstract = {We study the tunneling conductance of a ballistic normal metal/ferromagnet/spin-triplet superconductor junction using the extended Blonder-Tinkham-Klapwijk formalism as a model for a c-axis-oriented Au/SrRuO3/Sr2RuO4 junction. We compare chiral p-wave (CPW) and helical p-wave (HPW) pair potentials, combined with ferromagnet magnetization directions parallel and perpendicular to the interface. For fixed θM, where θM is a direction of magnetization in the ferromagnet measured from the c axis, the tunneling conductances of CPW and HPW clearly show different voltage dependencies. It is found that the cases where the d vector is perpendicular to the magnetization direction (CPW with θM=π/2 and HPW with θM=0) are identical. The obtained results serve as a guide to determine the pairing symmetry of the spin-triplet superconductor Sr2RuO4. © 2018 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Barber2018,

title = {Resistivity in the Vicinity of a van Hove Singularity: Sr2RuO4 under Uniaxial Pressure},

author = {M E Barber and A S Gibbs and Y Maeno and A P Mackenzie and C W Hicks},

doi = {10.1103/PhysRevLett.120.076602},

year  = {2018},

date = {2018-01-01},

journal = {Physical Review Letters},

volume = {120},

number = {7},

abstract = {We report the results of a combined study of the normal-state resistivity and superconducting transition temperature Tc of the unconventional superconductor Sr2RuO4 under uniaxial pressure. There is strong evidence that, as well as driving Tc through a maximum at ∼3.5 K, compressive strains of nearly 1% along the crystallographic [100] axis drive the γ Fermi surface sheet through a van Hove singularity, changing the temperature dependence of the resistivity from T2 above, and below the transition region to T1.5 within it. This occurs in extremely pure single-crystals in which the impurity contribution to the resistivity is <100 nΩ cm, so our study also highlights the potential of uniaxial pressure as a more general probe of this class of physics in clean systems. © 2018 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Sedeki2018,

title = {Influence of carrier lifetime on quantum criticality and superconducting Tc of (TMTSF) 2ClO4},

author = {A Sedeki and P Auban-Senzier and S Yonezawa and C Bourbonnais and D Jerome},

doi = {10.1103/PhysRevB.98.115111},

year  = {2018},

date = {2018-01-01},

journal = {Physical Review B},

volume = {98},

number = {11},

abstract = {This work presents and analyzes electrical resistivity data on the organic superconductor (TMTSF)2ClO4 and their anion-substituted alloys (TMTSF)2(ClO4)1-x(ReO4)x along the least conducting câ axis. Nonmagnetic disorder introduced by finite size domains of anion ordering on non-Fermi-liquid character of resistivity is investigated near the conditions of quantum criticality taking place at x=0. The evolution of the T-linear resistivity term with anion disorder shows a limited decrease in contrast with the complete suppression of the critical temperature Tc as expected for unconventional superconductivity beyond a threshold value of x. The resulting breakdown of scaling between both quantities is compared to the theoretical predictions of a linearized Boltzmann equation combined to the scaling theory of umklapp scattering in the presence of disorder-induced pair breaking for the carriers. The theory shows that quantum antiferromagnetic fluctuations, which are at the core of unconventional Cooper pairing and inelastic scattering of T-linear resistivity in these systems, are weakly affected by disorder while the phase coherence responsible for a finite Tc can be completely suppressed. © 2018 American Physical Society.},

note = {cited By 0},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yonezawa2018,

title = {Crossover from impurity-controlled to granular superconductivity in (TMTSF)2 ClO4},

author = {S Yonezawa and C A Marrache-Kikuchi and K Bechgaard and D Jérome},

doi = {10.1103/PhysRevB.97.014521},

year  = {2018},

date = {2018-01-01},

journal = {Physical Review B},

volume = {97},

number = {1},

abstract = {Using a proper cooling procedure, a controllable amount of nonmagnetic structural disorder can be introduced at low temperature in (TMTSF)2ClO4. Here we performed simultaneous measurements of transport and magnetic properties of (TMTSF)2ClO4 in its normal and superconducting states, while finely covering three orders of magnitude of the cooling rate around the anion ordering temperature. Our result reveals, with increasing density of disorder, the existence of a crossover between homogeneous defect-controlled d-wave superconductivity and granular superconductivity. At slow cooling rates, with small amount of disorder, the evolution of superconducting properties is well described with the Abrikosov-Gorkov theory, providing further confirmation of non-s-wave pairing in this compound. In contrast, at fast cooling rates, zero resistance and diamagnetic shielding are achieved through a randomly distributed network of superconducting puddles embedded in a normal conducting background and interconnected by proximity effect coupling. The temperature dependence of the ac complex susceptibility reveals features typical for a network of granular superconductors. This makes (TMTSF)2ClO4 a model system for granular superconductivity where the grain size and their concentration are tunable within the same sample. © 2018 American Physical Society.},

note = {cited By 5},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitagawa2018b,

title = {Nematic transition and highly two-dimensional superconductivity in BaTi2Bi2 O revealed by Bi 209 -nuclear magnetic resonance/nuclear quadrupole resonance measurements},

author = {S Kitagawa and K Ishida and W Ishii and T Yajima and Z Hiroi},

doi = {10.1103/PhysRevB.98.220507},

year  = {2018},

date = {2018-01-01},

journal = {Physical Review B},

volume = {98},

number = {22},

abstract = {In this Rapid Communication, a set of Bi209-nuclear magnetic resonance (NMR)/nuclear quadrupole resonance (NQR) measurements has been performed to investigate the physical properties of superconducting (SC) BaTi2Bi2O from a microscopic point of view. The NMR and NQR spectra at 5 K can be reproduced with a nonzero in-plane anisotropic parameter η, indicating the breaking of the in-plane fourfold symmetry at the Bi site without any magnetic order, i.e., "the electronic nematic state." In the SC state, the nuclear spin-lattice relaxation rate divided by temperature, 1/T1T, does not change even below Tc, while a clear SC transition was observed with a diamagnetic signal. This observation can be attributed to the strong two dimensionality in BaTi2Bi2O. Comparing the NMR/NQR results among BaTi2Pn2O (Pn=As, Sb, and Bi), it was found that the normal and SC properties of BaTi2Bi2O were considerably different from those of BaTi2Sb2O and BaTi2As2O, which might explain the two-dome structure of Tc in this system. © 2018 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Smidman20182930,

title = {Interplay between unconventional superconductivity and heavy-fermion quantum criticality: CeCu2Si2 versus YbRh2Si2},

author = {M Smidman and O Stockert and J Arndt and G M Pang and L Jiao and H Q Yuan and H A Vieyra and S Kitagawa and K Ishida and K Fujiwara and T C Kobayashi and E Schuberth and M Tippmann and L Steinke and S Lausberg and A Steppke and M Brando and H Pfau and U Stockert and P Sun and S Friedemann and S Wirth and C Krellner and S Kirchner and E M Nica and R Yu and Q Si and F Steglich},

doi = {10.1080/14786435.2018.1511070},

year  = {2018},

date = {2018-01-01},

journal = {Philosophical Magazine},

volume = {98},

number = {32},

pages = {2930-2963},

abstract = {In this paper the low-temperature properties of two isostructural canonical heavy-fermion compounds are contrasted with regards to the interplay between antiferromagnetic (AF) quantum criticality and superconductivity. For CeCu2Si2, fully-gapped d-wave superconductivity forms in the vicinity of an itinerant three-dimensional heavy-fermion spin-density-wave (SDW) quantum critical point (QCP). Inelastic neutron scattering results highlight that both quantum critical SDW fluctuations as well as Mott-type fluctuations of local magnetic moments contribute to the formation of Cooper pairs in CeCu2Si2. In YbRh2Si2, superconductivity appears to be suppressed at T ⪆ 10 mK by AF order (TN = 70 mK). Ultra-low temperature measurements reveal a hybrid order between nuclear and 4f-electronic spins, which is dominated by the Yb-derived nuclear spins, to develop at TA slightly above 2 mK. The hybrid order turns out to strongly compete with the primary 4f-electronic order and to push the material towards its QCP. Apparently, this paves the way for heavy-fermion superconductivity to form at Tc = 2 mK. Like the pressure – induced QCP in CeRhIn5, the magnetic field – induced one in YbRh2Si2 is of the local Kondo-destroying variety which corresponds to a Mott-type transition at zero temperature. Therefore, these materials form the link between the large family of about fifty low-T unconventional heavy – fermion superconductors and other families of unconventional superconductors with higher Tcs, notably the doped Mott insulators of the cuprates, organic charge-transfer salts and some of the Fe-based superconductors. Our study suggests that heavy-fermion superconductivity near an AF QCP is a robust phenomenon. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitagawa2018c,

title = {Evidence for the Presence of the Fulde-Ferrell-Larkin-Ovchinnikov State in CeCu2Si2 Revealed Using Cu 63 NMR},

author = {S Kitagawa and G Nakamine and K Ishida and H S Jeevan and C Geibel and F Steglich},

doi = {10.1103/PhysRevLett.121.157004},

year  = {2018},

date = {2018-01-01},

journal = {Physical Review Letters},

volume = {121},

number = {15},

abstract = {Nuclear magnetic resonance measurements were performed on CeCu2Si2 in the presence of a magnetic field close to the upper critical field μ0Hc2 in order to investigate its superconducting (SC) properties near pair-breaking fields. In lower fields, the Knight shift and nuclear spin-lattice relaxation rate divided by temperature 1/T1T abruptly decreased below the SC transition temperature Tc(H), a phenomenon understood within the framework of conventional spin-singlet superconductivity. In contrast, 1/T1T was enhanced just below Tc(H) and exhibited a broad maximum when magnetic fields close to μ0Hc2(0) were applied parallel or perpendicular to the c axis; although the Knight shift decreased just below Tc(H). This enhancement of 1/T1T, which was recently observed in the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2, suggests the presence of high-density Andreev bound states in the inhomogeneous SC region, a hallmark of the Fulde-Ferrell-Larkin-Ovchinnikov phase. © 2018 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yamamoto20181566,

title = {Selective Hydride Occupation in BaVO3-xHx (0.3 ≤ × ≤ 0.8) with Faceand Corner-Shared Octahedra},

author = {T Yamamoto and K Shitara and S Kitagawa and A Kuwabara and M Kuroe and K Ishida and M Ochi and K Kuroki and K Fujii and M Yashima and C M Brown and H Takatsu and C Tassel and H Kageyama},

doi = {10.1021/acs.chemmater.7b04571},

year  = {2018},

date = {2018-01-01},

journal = {Chemistry of Materials},

volume = {30},

number = {5},

pages = {1566-1574},

abstract = {A growing number of transition metal oxyhydrides have recently been reported, but they are all confined to perovskite-related structures with corner-shared octahedra. Using high pressure synthesis, we have obtained vanadium oxyhydrides BaVO3-xHx (0.3 ≤ x ≤ 0.8) with a 6H-type hexagonal layer structure consisting of face-shared as well as corner-shared octahedra. Synchrotron X-ray and neutron diffraction measurements revealed that, in BaVO2.7H0.3, H- anions are located selectively at the face-shared sites, as supported by DFT calculations, while BaVO2.2H0.8 contains H- anions at both sites though the face-shared preference is partially retained. The selective hydride occupation for BaVO2.7H0.3 appears to suppress electron hopping along the c axis, making this material a quasi-two-dimensional metal characterized by anomalous temperature dependence of the electrical resistivity and strong antiferromagnetic fluctuations. In contrast, the anion disordered BaVO3-xHx in hexagonal (x ≈ 0.8) and cubic (x ≈ 0.9) forms exhibits a semiconducting behavior. This study offers a wide opportunity to develop transition metal oxyhydrides having various polyhedral linkages, along with site preference of H/O anions, aimed at finding interesting phenomena. © 2018 American Chemical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Manago2018,

title = {Single ferromagnetic fluctuations in UCoGe revealed by Ge 73 - And Co 59 -NMR studies},

author = {M Manago and K Ishida and D Aoki},

doi = {10.1103/PhysRevB.97.075130},

year  = {2018},

date = {2018-01-01},

journal = {Physical Review B},

volume = {97},

number = {7},

abstract = {Ge73 and Co59 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been performed on a Ge73-enriched single-crystalline sample of the ferromagnetic superconductor UCoGe in the paramagnetic state. The Ge73 NQR parameters deduced from NQR and NMR are close to those of another isostructural ferromagnetic superconductor URhGe. The Knight shifts of the Ge and Co sites are well scaled to each other when the magnetic field is parallel to the b or c axis. The hyperfine coupling constants of Ge are estimated to be close to those of Co. The large difference of spin susceptibilities between the a and b axes could lead to the different response of the superconductivity and ferromagnetism with the field parallel to these directions. The temperature dependence of the nuclear spin-lattice relaxation rates 1/T1 at the two sites is similar to each other above 5 K. These results indicate that the itinerant U-5f electrons are responsible for the ferromagnetism in this compound, consistent with previous studies. The similarities and differences in the three ferromagnetic superconductors are discussed. © 2018 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitagawa2018d,

title = {Spatially inhomogeneous superconducting state near Hc2 in UPd2Al3},

author = {S Kitagawa and R Takaki and M Manago and K Ishida and N K Sato},

doi = {10.7566/JPSJ.87.013701},

year  = {2018},

date = {2018-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {87},

number = {1},

abstract = {We have performed 27Al-NMR measurements on single-crystalline UPd2Al3 with the field parallel to the c-axis to investigate the superconducting (SC) properties near the upper critical field of superconductivity Hc2. The broadening of the NMR linewidth below 14K indicates the appearance of the internal field at the Al site, which originates from the antiferromagnetically ordered moments of U 5 f electrons. In the SC state well below μ0Hc2 = 3.4 T, the broadening of the NMR linewidth due to the SC diamagnetism and a decrease in the Knight shift are observed, which are wellunderstood by the framework of spin-singlet superconductivity. In contrast, the Knight shift does not change below Tc(H), and the NMR spectrum is broadened symmetrically in the SC state in the field range of 3 T < μ0H < μ0Hc2. The unusual NMR spectrum near Hc2 suggests that a spatially inhomogeneous SC state such as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state would be realized. © 2018 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Shi2018,

title = {High-field superconductivity on iron chalcogenide FeSe},

author = {A Shi and S Kitagawa and K Ishida and A E Böhmer and C Meingast and T Wolf},

doi = {10.7566/JPSJ.87.065002},

year  = {2018},

date = {2018-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {87},

number = {6},

abstract = {We have performed ac-susceptibility and77Se-NMR measurements on single-crystal FeSe in the field range from 12.5 to 14.75T below 1.6K in order to investigate the superconducting properties of the B phase. Our results show that although superconductivity persists beyond the A–B transition line (H+), the broadening of the 77Se-NMR linewidth arising from the superconducting diamagnetic effect decreases at around H+, suggesting that superconducting character is changed at H+. © 2018 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Shi2018b,

title = {Pseudogap behavior of the nuclear spin-lattice relaxation rate in FeSe probed by 77Se-NMR},

author = {A Shi and T Arai and S Kitagawa and T Yamanaka and K Ishida and A E Böhmer and C Meingast and T Wolf and M Hirata and T Sasaki},

doi = {10.7566/JPSJ.87.013704},

year  = {2018},

date = {2018-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {87},

number = {1},

abstract = {We conducted 77Se-nuclear magnetic resonance studies of the iron-based superconductor FeSe in magnetic fields of 0.6 to 19 T to investigate the superconducting and normal-state properties. The nuclear spin-lattice relaxation rate divided by the temperature (T1T)-1 increases below the structural transition temperature Ts but starts to be suppressed below T∗, well above the superconducting transition temperature Tc(H), resulting in a broad maximum of (T1T)-1 at Tp(H). This is similar to the pseudogap behavior in optimally doped cuprate superconductors. Because T∗ and Tp(H) decrease in the same manner as Tc(H) with increasing H, the pseudogap behavior in FeSe is ascribed to superconducting fluctuations, which presumably originate from the theoretically predicted preformed pair above Tc(H). © 2018 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yasui2017,

title = {Little-Parks oscillations with half-quantum fluxoid features in Sr_{2}RuO_{4} microrings},

author = {Y Yasui and K Lahabi and M S Anwar and Y Nakamura and S Yonezawa and T Terashima and J Aarts and Y Maeno},

doi = {10.1103/PhysRevB.96.180507},

year  = {2017},

date = {2017-11-27},

journal = {Physical Review B},

volume = {96},

number = {18},

abstract = {In a microring of a superconductor with a spin-triplet equal-spin pairing state, a fluxoid, a combined object of magnetic flux and circulating supercurrent, can penetrate as half-integer multiples of the flux quantum. A candidate material to investigate such half-quantum fluxoids is Sr 2 RuO 4 . We fabricated Sr 2 RuO 4 microrings using single crystals and measured their resistance behavior under magnetic fields controlled with a three-axis vector magnet. Proper Little-Parks oscillations in the magnetovoltage as a function of an axially applied field, associated with fluxoid quantization, are clearly observed using bulk single-crystalline superconductors. We then performed magnetovoltage measurements with additional in-plane magnetic fields. By carefully analyzing both the voltages V+ (V-) measured at positive (negative) current, we find that, above an in-plane threshold field of about 10 mT, the magnetovoltage maxima convert to minima. We interpret this behavior as the peak splitting expected for the half-quantum fluxoid states. © 2017 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mackenzie2017,

title = {Even odder after twenty-three years: The superconducting order parameter puzzle of Sr2RuO4},

author = {A P Mackenzie and T Scaffidi and C W Hicks and Y Maeno},

doi = {10.1038/s41535-017-0045-4},

year  = {2017},

date = {2017-01-01},

journal = {npj Quantum Materials},

volume = {2},

number = {1},

abstract = {In this short review, we aim to provide a topical update on the status of efforts to understand the superconductivity of Sr2RuO4. We concentrate on efforts to identify a superconducting order parameter symmetry that is compatible with all the major pieces of experimental knowledge of the material, and highlight some major discrepancies that have become even clearer in recent years. As the pun in the title suggests, we have tried to start the discussion from scratch, making no assumptions even about fundamental issues such as the parity of the superconducting state. We conclude that no consensus is currently achievable in Sr2RuO4, and that the reasons for this go to the heart of how well some of the key probes of unconventional superconductivity are really understood. This is, therefore, a puzzle that merits continued in-depth study. © 2017 The Author(s).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Sow20171084,

title = {Current-induced strong diamagnetism in the Mott insulator Ca2RuO4},

author = {C Sow and S Yonezawa and S Kitamura and T Oka and K Kuroki and F Nakamura and Y Maeno},

doi = {10.1126/science.aah4297},

year  = {2017},

date = {2017-01-01},

journal = {Science},

volume = {358},

number = {6366},

pages = {1084-1087},

abstract = {Mott insulators can host a surprisingly diverse set of quantum phenomena when their frozen electrons are perturbed by various stimuli. Superconductivity, metal-insulator transition, and colossal magnetoresistance induced by element substitution, pressure, and magnetic field are prominent examples. Here we report strong diamagnetism in the Mott insulator calcium ruthenate (Ca2RuO4) induced by dc electric current. The application of a current density of merely 1 ampere per centimeter squared induces diamagnetism stronger than that in other nonsuperconducting materials. This change is coincident with changes in the transport properties as the system becomes semimetallic. These findings suggest that dc current may be a means to control the properties of materials in the vicinity of a Mott insulating transition. © 2017, American Association for the Advancement of Science. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Sakuma2017,

title = {Investigation of the vortex states of Sr2RuO4-Ru eutectic microplates using DC-SQUIDs},

author = {D Sakuma and Y Nago and R Ishiguro and S Kashiwaya and S Nomura and K Kono and Y Maeno and H Takayanagi},

doi = {10.7566/JPSJ.86.114708},

year  = {2017},

date = {2017-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {86},

number = {11},

abstract = {We investigated the magnetic properties of a Sr2RuO4-Ru eutectic microplate containing a single Ru-inclusion using micrometer-sized DC-SQUIDs (direct-current superconducting quantum interference devices). A phase frustration at the interface between chiral p-wave superconducting Sr2RuO4 and s-wave superconducting Ru is expected to cause novel magnetic vortex states such as the spontaneous Ru-center vortex under zero magnetic field [as reported by H. Kaneyasu and M. Sigrist, J. Phys. Soc. Jpn. 79, 053706 (2010)]. Our experimental results show no positive evidence for such a spontaneous vortex state. However, in an applied field, an abrupt change in the magnetic flux distribution was observed at a superconducting transition of Ru. The flux distribution is clarified by comparing our experimental results with electromagnetic field simulations in our sample geometry. We discuss the transition of the vortex states and the superconducting coupling at the Sr2RuO4=Ru interface © 2017 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kuhn2017,

title = {Anisotropy and multiband superconductivity in Sr2RuO4 determined by small-angle neutron scattering studies of the vortex lattice},

author = {S J Kuhn and W Morgenlander and E R Louden and C Rastovski and W J Gannon and H Takatsu and D C Peets and Y Maeno and C D Dewhurst and J Gavilano and M R Eskildsen},

doi = {10.1103/PhysRevB.96.174507},

year  = {2017},

date = {2017-01-01},

journal = {Physical Review B},

volume = {96},

number = {17},

abstract = {Despite numerous studies the exact nature of the order parameter in superconducting Sr2RuO4 remains unresolved. We have extended previous small-angle neutron scattering studies of the vortex lattice in this material to a wider field range, higher temperatures, and with the field applied close to both the (100) and (110) basal plane directions. Measurements at high field were made possible by the use of both spin polarization and analysis to improve the signal-to-noise ratio. Rotating the field towards the basal plane causes a distortion of the square vortex lattice observed for H(001) and also a symmetry change to a distorted triangular symmetry for fields close to (100).The vortex lattice distortion allows us to determine the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane, yielding a value of ∼60 at low temperature and low to intermediate fields. This greatly exceeds the upper critical field anisotropy of ∼20 at low temperature, reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects on the unpaired quasiparticles in the vortex cores are observed, but a direct detection lies below the measurement sensitivity. The superconducting anisotropy is found to be independent of temperature but increases for fields 1 T, indicating multiband superconductvity in Sr2RuO4. Finally, the temperature dependence of the scattered intensity provides further support for gap nodes or deep minima in the superconducting gap. © 2017 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Wang2017799,

title = {Quasiparticle interference and strong electron-mode coupling in the quasi-one-dimensional bands of Sr 2 RuO 4},

author = {Z Wang and D Walkup and P Derry and T Scaffdi and M Rak and S Vig and A Kogar and I Zeljkovic and A Husain and L H Santos and Y Wang and A Damascelli and Y Maeno and P Abbamonte and E Fradkin and V Madhavan},

doi = {10.1038/NPHYS4107},

year  = {2017},

date = {2017-01-01},

journal = {Nature Physics},

volume = {13},

number = {8},

pages = {799-805},

abstract = {The single-layered ruthenate Sr 2 RuO 4 is presented as a potential spin-triplet superconductor with an order parameter that may break time-reversal invariance and host half-quantized vortices with Majorana zero modes. Although the actual nature of the superconducting state is still a matter of controversy, it is believed to condense from a metallic state that is well described by a conventional Fermi liquid. In this work we use a combination of Fourier transform scanning tunnelling spectroscopy (FT-STS) and momentum-resolved electron energy loss spectroscopy (M-EELS) to probe interaction effects in the normal state of Sr 2 RuO 4 . Our high-resolution FT-STS data show signatures of the β-band with a distinctly quasi-one-dimensional (1D) character. The band dispersion reveals surprisingly strong interaction effects that dramatically renormalize the Fermi velocity, suggesting that the normal state of Sr 2 RuO 4 is that of a 'correlated metal' where correlations are strengthened by the quasi-1D nature of the bands. In addition, kinks at energies of approximately 10 meV, 38 meV and 70 meV are observed. By comparing STM and M-EELS data we show that the two higher energy features arise from coupling with collective modes. The strong correlation effects and the kinks in the quasi-1D bands could provide important information for understanding the superconducting state. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Anwar2017,

title = {Multicomponent order parameter superconductivity of Sr2RuO4 revealed by topological junctions},

author = {M S Anwar and R Ishiguro and T Nakamura and M Yakabe and S Yonezawa and H Takayanagi and Y Maeno},

doi = {10.1103/PhysRevB.95.224509},

year  = {2017},

date = {2017-01-01},

journal = {Physical Review B},

volume = {95},

number = {22},

abstract = {Single crystals of the Sr2RuO4-Ru eutectic system are known to exhibit enhanced superconductivity at 3 K in addition to the bulk superconductivity of Sr2RuO4 at 1.5 K. The 1.5 K phase is believed to be a spin-triplet, chiral p-wave state with a multicomponent order parameter, giving rise to chiral domain structure. In contrast, the 3 K phase is attributable to enhanced superconductivity of Sr2RuO4 in the strained interface region between Ru inclusion of a few to tens of micrometers in size and the surrounding Sr2RuO4. We investigate the dynamic behavior of a topological junction, where a superconductor is surrounded by another superconductor. Specifically, we fabricated Nb/Ru/Sr2RuO4 topological superconducting junctions, in which the difference in phase winding between the s-wave superconductivity in Ru microislands induced from Nb and the superconductivity of Sr2RuO4 mainly governs the junction behavior. Comparative results of the asymmetry, hysteresis, and noise in junctions with different sizes, shapes, and configurations of Ru inclusions are explained by the chiral domain-wall motion in these topological junctions. Furthermore, a striking difference between the 1.5 and 3 K phases is clearly revealed: the large noise in the 1.5 K phase sharply disappears in the 3 K phase. These results confirm the multicomponent order-parameter superconductivity of the bulk Sr2RuO4, consistent with the chiral p-wave state, and the proposed nonchiral single-component superconductivity of the 3 K phase. © 2017 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kunkemöller2017,

title = {Absence of a Large Superconductivity-Induced Gap in Magnetic Fluctuations of Sr2RuO4},

author = {S Kunkemöller and P Steffens and P Link and Y Sidis and Z Q Mao and Y Maeno and M Braden},

doi = {10.1103/PhysRevLett.118.147002},

year  = {2017},

date = {2017-01-01},

journal = {Physical Review Letters},

volume = {118},

number = {14},

abstract = {Inelastic neutron scattering experiments on Sr2RuO4 determine the spectral weight of the nesting induced magnetic fluctuations across the superconducting transition. There is no observable change at the superconducting transition down to an energy of ∼0.35 meV, which is well below the 2Δ values reported in several tunneling experiments. At this and higher energies magnetic fluctuations clearly persist in the superconducting state. Only at energies below ∼0.3 meV can evidence for partial suppression of spectral weight in the superconducting state be observed. This strongly suggests that the one-dimensional bands with the associated nesting fluctuations do not form the active, highly gapped bands in the superconducting pairing in Sr2RuO4. © 2017 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hassinger2017,

title = {Vertical line nodes in the superconducting gap structure of Sr2RuO4},

author = {E Hassinger and P Bourgeois-Hope and H Taniguchi and S René de Cotret and G Grissonnanche and M S. Anwar and Y Maeno and N Doiron-Leyraud and L Taillefer},

doi = {10.1103/PhysRevX.7.011032},

year  = {2017},

date = {2017-01-01},

journal = {Physical Review X},

volume = {7},

number = {1},

abstract = {There is strong experimental evidence that the superconductor Sr2RuO4 has a chiral p-wave order parameter. This symmetry does not require that the associated gap has nodes, yet specific heat, ultrasound, and thermal conductivity measurements indicate the presence of nodes in the superconducting gap structure of Sr2RuO4. Theoretical scenarios have been proposed to account for the existence of deep minima or accidental nodes (minima tuned to zero or below by material parameters) within a p-wave state. Other scenarios propose chiral d-wave and f-wave states, with horizontal and vertical line nodes, respectively. To elucidate the nodal structure of the gap, it is essential to know whether the lines of nodes (or minima) are vertical (parallel to the tetragonal c axis) or horizontal (perpendicular to the c axis). Here, we report thermal conductivity measurements on single crystals of Sr2RuO4 down to 50 mK for currents parallel and perpendicular to the c axis. We find that there is substantial quasiparticle transport in the T = 0 limit for both current directions. A magnetic field H immediately excites quasiparticles with velocities both in the basal plane and in the c direction. Our data down to Tc/30 and down to Hc2=100 show no evidence that the nodes are in fact deep minima. Relative to the normal state, the thermal conductivity of the superconducting state is found to be very similar for the two current directions, from H = 0 to H = Hc2. These findings show that the gap structure of Sr2RuO4 consists of vertical line nodes. This rules out a chiral d-wave state. Given that the c-axis dispersion (warping) of the Fermi surface in Sr2RuO4 varies strongly from sheet to sheet, the small a - c anisotropy suggests that the line nodes are present on all three sheets of the Fermi surface. If imposed by symmetry, vertical line nodes would be inconsistent with a p-wave order parameter for Sr2RuO4. To reconcile the gap structure revealed by our data with a p-wave state, a mechanism must be found that produces accidental line nodes in Sr2RuO4.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yonezawa2017123,

title = {Thermodynamic evidence for nematic superconductivity in Cu x Bi 2 Se 3},

author = {S Yonezawa and K Tajiri and S Nakata and Y Nagai and Z Wang and K Segawa and Y Ando and Y Maeno},

doi = {10.1038/nphys3907},

year  = {2017},

date = {2017-01-01},

journal = {Nature Physics},

volume = {13},

number = {2},

pages = {123-126},

abstract = {In condensed matter physics, spontaneous symmetry breaking has been a key concept, and discoveries of new types of broken symmetries have greatly increased our understanding of matter 1,2 . Recently, electronic nematicity, novel spontaneous rotational-symmetry breaking leading to an emergence of a special direction in electron liquids, has been attracting significant attention 3-6 . Here, we show bulk thermodynamic evidence for nematic superconductivity, in which the nematicity emerges in the superconducting gap amplitude, in Cu x Bi 2 Se 3 . Based on high-resolution calorimetry of single-crystalline samples under accurate two-axis control of the magnetic field direction, we discovered clear two-fold symmetry in the specific heat and in the upper critical field despite the trigonal symmetry of the lattice. Nematic superconductivity for this material should possess a unique topological nature associated with odd parity 7-9 . Thus, our findings establish a new class of spontaneously symmetry-broken states of matter-namely, odd-parity nematic superconductivity. © 2017 Macmillan Publishers Limited.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Steppke2017,

title = {Strong peak in Tc of Sr2RuO4 under uniaxial pressure},

author = {A Steppke and L Zhao and M E Barber and T Scaffidi and F Jerzembeck and H Rosner and A S Gibbs and Y Maeno and S H Simon and A P Mackenzie and C W Hicks},

doi = {10.1126/science.aaf9398},

year  = {2017},

date = {2017-01-01},

journal = {Science},

volume = {355},

number = {6321},

abstract = {Sr2RuO4 is an unconventional superconductor that has attracted widespread study because of its high purity and the possibility that its superconducting order parameter has odd parity.We study the dependence of its superconductivity on anisotropic strain. Applying uniaxial pressures of up to ∼1 gigapascals along a h100i direction (a axis) of the crystal lattice results in the transition temperature (Tc) increasing from1.5 kelvin in the unstrainedmaterial to 3.4 kelvin at compression by ≈0.6%, and then falling steeply. Calculations give evidence that the observed maximum Tc occurs at or near a Lifshitz transition when the Fermi level passes through a Van Hove singularity, and open the possibility that the highly strained},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitagawa2017,

title = {Magnetic and superconducting properties of an S -type single-crystal CeCu2Si2 probed by Cu 63 nuclear magnetic resonance and nuclear quadrupole resonance},

author = {S Kitagawa and T Higuchi and M Manago and T Yamanaka and K Ishida and H S Jeevan and C Geibel},

doi = {10.1103/PhysRevB.96.134506},

year  = {2017},

date = {2017-01-01},

journal = {Physical Review B},

volume = {96},

number = {13},

abstract = {We have performed Cu63 nuclear-magnetic-resonance/nuclear-quadrupole-resonance measurements to investigate the magnetic and superconducting (SC) properties on a "superconductivity dominant" (S-type) single crystal of CeCu2Si2. Although the development of antiferromagnetic (AFM) fluctuations down to 1 K indicated that the AFM criticality was close, Korringa behavior was observed below 0.8 K, and no magnetic anomaly was observed above Tc∼0.6 K. These behaviors were expected in S-type CeCu2Si2. The temperature dependence of the nuclear spin-lattice relaxation rate 1/T1 at zero field was almost identical to that in the previous polycrystalline samples down to 130 mK, but the temperature dependence deviated downward below 120 mK. In fact, 1/T1 in the SC state could be fitted with the two-gap s±-wave model rather than the two-gap s++-wave model down to 90 mK. Under magnetic fields, the spin susceptibility in both directions clearly decreased below Tc, which is indicative of the formation of spin-singlet pairing. The residual part of the spin susceptibility was understood by the field-induced residual density of states evaluated from 1/T1T, which was ascribed to the effect of the vortex cores. No magnetic anomaly was observed above the upper critical field Hc2, but the development of AFM fluctuations was observed, indicating that superconductivity was realized in strong AFM fluctuations. © 2017 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yamanaka2017,

title = {Magnetic and superconducting properties of a heavy-fermion CeCoIn5 epitaxial film probed by nuclear quadrupole resonance},

author = {T Yamanaka and M Shimozawa and H Shishido and S Kitagawa and H Ikeda and T Shibauchi and T Terashima and Y Matsuda and K Ishida},

doi = {10.1103/PhysRevB.96.060507},

year  = {2017},

date = {2017-01-01},

journal = {Physical Review B},

volume = {96},

number = {6},

abstract = {Since the progress in the fabrication techniques of thin films of exotic materials such as strongly correlated heavy-fermion compounds, microscopic studies of the magnetic and electronic properties inside the films have been needed. Herein, we report the observation of In115 nuclear quadrupole resonance (NQR) in an epitaxial film of the heavy-fermion superconductor CeCoIn5, for which the microscopic field gradient within the unit cell as well as magnetic and superconducting properties at zero field are evaluated. We find that the nuclear spin-lattice relaxation rate in the film is in excellent agreement with that of bulk crystals, whereas the NQR spectra show noticeable shifts and significant broadening indicating a change in the electric-field distribution inside the film. The analysis implies a displacement of In layers in the film, which, however, does not affect the magnetic fluctuations and superconducting pairing. This implies that inhomogeneity of the electronic field gradient in the film sample causes no pair-breaking effect. © 2017 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Manago2017,

title = {Absence of the Pauli-paramagnetic limit in a superconducting U6Co},

author = {M Manago and K Ishida and D Aoki},

doi = {10.7566/JPSJ.86.073701},

year  = {2017},

date = {2017-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {86},

number = {7},

abstract = {We performed 59Co nuclear magnetic resonance (NMR) measurements of single-crystalline U6Co. There is a small decrease in the Knight shift in the superconducting (SC) state, but this change mainly arises from the SC diamagnetic effect. The negligible change of the spin part of the Knight shift, together with the absence of the Pauli-paramagnetic effect in the SC U6Co, is understood as a consequence of the small spin susceptibility. The nuclear spin–lattice relaxation rate 1/T1 is also measured in the SC state under the magnetic field, and exhibits a tiny Hebel–Slichter peak just below the SC transition temperature and exponential behavior at lower temperatures. These behaviors are in agreement with the full-gap s-wave pairing in U6Co. ©2017 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Oudah2016,

title = {Superconductivity in the antiperovskite Dirac-metal oxide Sr3-x SnO},

author = {M Oudah and A Ikeda and J N Hausmann and S Yonezawa and T Fukumoto and S Kobayashi and M Sato and Y Maeno},

url = {https://arxiv.org/abs/1604.06238},

doi = {10.1038/ncomms13617},

year  = {2016},

date = {2016-12-12},

journal = {Nature Communications},

volume = {7},

pages = {13617},

abstract = {Investigations of perovskite oxides triggered by the discovery of high-temperature and unconventional superconductors have had crucial roles in stimulating and guiding the development of modern condensed-matter physics. Antiperovskite oxides are charge-inverted counterpart materials to perovskite oxides, with unusual negative ionic states of a constituent metal. No superconductivity was reported among the antiperovskite oxides so far. Here we present the first superconducting antiperovskite oxide Sr3-x SnO with the transition temperature of around 5 K. Sr3SnO possesses Dirac points in its electronic structure, and we propose from theoretical analysis a possibility of a topological odd-parity superconductivity analogous to the superfluid 3He-B in moderately hole-doped Sr3-x SnO. We envision that this discovery of a new class of oxide superconductors will lead to a rapid progress in physics and chemistry of antiperovskite oxides consisting of unusual metallic anions. © 2016 The Author(s).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jimenez-Segura2016,

title = {Effect of delithiation on the dimer transition of the honeycomb-lattice ruthenate Li2-xRuO3},

author = {M -P Jimenez-Segura and A Ikeda and S A J Kimber and C Giacobbe and S Yonezawa and Y Maeno},

url = {https://arxiv.org/abs/1603.08764},

doi = {10.1103/PhysRevB.94.115163},

year  = {2016},

date = {2016-09-29},

journal = {Physical Review B},

volume = {94},

number = {11},

pages = {115163},

abstract = {The honeycomb-lattice ruthenate Li2RuO3 is made heavily Li deficient by chemical oxidation by iodine. The delithiation induces a different phase Li2-xRuO3, the "D phase," with superlattice. For the first time we disclose the magnetic and structural properties of the D phase in the dimer-solid state. The low-temperature magnetic susceptibility and the bond lengths indicate a bonding configuration consisting of both Ru4+-Ru4+ and Ru5+-Ru5+ dimers. © 2016 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jimenez-Segura2016b,

title = {Effect of disorder on the dimer transition of the honeycomb-lattice compound Li2RuO3},

author = {M -P Jimenez-Segura and A Ikeda and S Yonezawa and Y Maeno},

url = {https://arxiv.org/abs/1602.06396},

doi = {10.1103/PhysRevB.93.075133},

year  = {2016},

date = {2016-02-18},

journal = {Physical Review B},

volume = {93},

number = {7},

pages = {075133},

abstract = {We report the dependence of magnetic properties on the crystalline disorder in Li2RuO3 with Ru honeycomb lattice. This oxide exhibits unconventional Ru-dimer transition below Td∼540 K. We demonstrate that the cell parameters, related to the coherence of the dimer formation, are strongly dependent on the synthesis procedure. We show that the magnetic behavior at the dimer transition is closely related to the lattice parameters. In particular, we revealed that samples with well-ordered dimers exhibit a first-order magnetic transition with the onset exceeding 550 K, higher than that reported previously. We discuss possible dimer configurations leading to this magnetolattice coupling. © 2016 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kondo2016,

title = {Orbital-Dependent Band Narrowing Revealed in an Extremely Correlated Hund's Metal Emerging on the Topmost Layer of Sr2RuO4},

author = {T Kondo and M Ochi and M Nakayama and H Taniguchi and S Akebi and K Kuroda and M Arita and S Sakai and H Namatame and M Taniguchi and Y Maeno and R Arita and S Shin},

doi = {10.1103/PhysRevLett.117.247001},

year  = {2016},

date = {2016-01-01},

journal = {Physical Review Letters},

volume = {117},

number = {24},

abstract = {We use a surface-selective angle-resolved photoemission spectroscopy and unveil the electronic nature on the topmost layer of Sr2RuO4 crystal, consisting of slightly rotated RuO6 octahedrons. The γ band derived from the 4dxy orbital is found to be about three times narrower than that for the bulk. This strongly contrasts with a subtle variation seen in the α and β bands derived from the one-dimensional 4dxz/yz. This anomaly is reproduced by the dynamical mean-field theory calculations, introducing not only the on-site Hubbard interaction but also the significant Hund's coupling. We detect a coherence-to-incoherence crossover theoretically predicted for Hund's metals, which has been recognized only recently. The crossover temperature in the surface is about half that of the bulk, indicating that the naturally generated monolayer of reconstructed Sr2RuO4 is extremely correlated and well isolated from the underlying crystal. © 2016 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Anwar2016,

title = {Direct penetration of spin-triplet superconductivity into a ferromagnet in Au/SrRuO3/Sr2 RuO4 junctions},

author = {M S Anwar and S R Lee and R Ishiguro and Y Sugimoto and Y Tano and S J Kang and Y J Shin and S Yonezawa and D Manske and H Takayanagi and T W Noh and Y Maeno},

doi = {10.1038/ncomms13220},

year  = {2016},

date = {2016-01-01},

journal = {Nature Communications},

volume = {7},

abstract = {Efforts have been ongoing to establish superconducting spintronics utilizing ferromagnet/inferconductor heterostructures. Previously reported devices are based on spin-singlet superconductors (SSCs), where the spin degree of freedom is lost. Spin-polarized supercurrent induction in ferromagnetic metals (FMs) is achieved even with SSCs, but only with the aid of interfacial complex magnetic structures, which severely affect information imprinted to the electron spin. Use of spin-triplet superconductors (TSCs) with spin-polarizable Cooper pairs potentially overcomes this difficulty and further leads to novel functionalities. Here, we report spin-triplet superconductivity induction into a FM SrRuO3 from a leading TSC candidate Sr2 RuO4, by fabricating microscopic devices using an epitaxial SrRuO3/Sr2 RuO4 hybrid. The differential conductance, exhibiting Andreev-reflection features with multiple energy scales up to around half tesla, indicates the penetration of superconductivity over a considerable distance of 15 nm across the SrRuO3 layer without help of interfacial complex magnetism. This demonstrates potential utility of FM/TSC devices for superspintronics. © 2016 The Author(s).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Manago2016,

title = {Anomalous magnetic fluctuations in superconducting Sr2RuO4 revealed by Ru 101 nuclear spin-spin relaxation},

author = {M Manago and T Yamanaka and K Ishida and Z Mao and Y Maeno},

doi = {10.1103/PhysRevB.94.144511},

year  = {2016},

date = {2016-01-01},

journal = {Physical Review B},

volume = {94},

number = {14},

abstract = {We carried out Ru101 nuclear quadrupole resonance (NQR) measurement on superconducting (SC) Sr 2 RuO 4 under zero magnetic field (H=0) and found that the nuclear spin-spin relaxation rate 1/T 2 is enhanced in the SC state. The 1/T 2 measurement in the SC state under H=0 is effective for detecting slow magnetic fluctuations parallel to the quantized axis of the nuclear spin. Our results indicate that low-energy magnetic fluctuations perpendicular to the RuO 2 plane emerge when the superconductivity sets in, which is consistent with the previous O17-NQR result that the nuclear spin-lattice relaxation rate 1/T1 of the in-plane O site exhibits anomalous behavior in the SC state. The enhancement of the magnetic fluctuations in the SC state is unusual and suggests that the fluctuations are related to the unconventional SC pairing. We suggest that this phenomenon is a consequence of the spin degrees of freedom of the spin-triplet pairing. © 2016 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nago2016b,

title = {Evolution of supercurrent path in Nb/Ru/Sr2RuO4 dc-SQUIDs},

author = {Y Nago and R Ishiguro and T Sakurai and M Yakabe and T Nakamura and S Yonezawa and S Kashiwaya and H Takayanagi and Y Maeno},

doi = {10.1103/PhysRevB.94.054501},

year  = {2016},

date = {2016-01-01},

journal = {Physical Review B},

volume = {94},

number = {5},

abstract = {Phase-sensitive measurements of direct-current superconducting quantum interference devices (dc-SQUIDs) composed of Sr2RuO4-Ru eutectic crystals have been performed to temperatures below a bulk Ru superconducting transition temperature at 0.49 K. A SQUID with Nb/Ru/Sr2RuO4 junctions fabricated on one Ru inclusion exhibits two distinct transitions due to the Ru superconducting transition and competition of proximity-induced superconducting gaps at the junctions. At sufficiently low temperatures, the SQUID interference patterns start to collapse with large phase shifts of the Fraunhofer patterns. This result indicates the influence of magnetic fluxes induced by large bias currents flowing in a strongly asymmetric supercurrent path. Such a large change in supercurrent path suggests superconducting phase mismatch between the s-wave and chiral p-wave states at the Ru/Sr2RuO4 interface. © 2016 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kikugawa2016,

title = {Superconducting subphase in the layered perovskite ruthenate Sr2RuO4 in a parallel magnetic field},

author = {N Kikugawa and T Terashima and S Uji and K Sugii and Y Maeno and D Graf and R Baumbach and J Brooks},

doi = {10.1103/PhysRevB.93.184513},

year  = {2016},

date = {2016-01-01},

journal = {Physical Review B},

volume = {93},

number = {18},

abstract = {Magnetic torque measurements using a microcantilever have been performed to investigate the superconducting phase of Sr2RuO4 down to 40 mK. For high-quality single crystals with the transition temperature (Tc) of 1.48-1.49 K, an abrupt jump of the torque signal is found near 1.5 T in field parallel to the conducting RuO2 planes below ∼0.8K. The jump corresponds to the first order transition recently revealed by magnetocaloric and magnetization measurements [Yonezawa, Phys. Rev. Lett. 110, 077003 (2013)PRLTAO0031-900710.1103/PhysRevLett.110.077003; Kittaka, Phys. Rev. B 90, 220502(R) (2014)PRBMDO1098-012110.1103/PhysRevB.90.220502]. Furthermore, weak diamagnetic and irreversible signals are found to persist above the first order transition up to 1.85 T. The result indicates the presence of a subphase boundary separating low- and high-field phases in the superconducting phase. The high-field subphase disappears when the field is tilted from the conducting planes only by a few degrees. Quantum oscillation measurements are also reported to clarify the strong sample-quality dependence of the high-field subphase. © 2016 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nago2016292,

title = {Development of Magnetization Measurement Devices Using Micro-dc-SQUIDs and a Sr2RuO4 Microplate},

author = {Y Nago and T Shinozaki and S Tsuchiya and R Ishiguro and H Kashiwaya and S Kashiwaya and S Nomura and K Kono and H Takayanagi and Y Maeno},

doi = {10.1007/s10909-016-1530-z},

year  = {2016},

date = {2016-01-01},

journal = {Journal of Low Temperature Physics},

volume = {183},

number = {3-4},

pages = {292-299},

abstract = {We developed high-sensitivity magnetization measurement devices composed of micro-dc-SQUIDs and a superconducting Sr (Formula presented.) RuO (Formula presented.) microplate, aiming to investigate novel magnetic properties related to a spin-triplet chiral p-wave superconductor with a mesoscopic size. Micron-sized dc-SQUID was fabricated by thin Al electrodes, and the SQUID structure was improved to prevent magnetic fluxes from intruding into SQUID electrodes. A Sr (Formula presented.) RuO (Formula presented.) superconducting microplate was fabricated into the size as small as the SQUID loop using a focused ion beam and directly mounted on the SQUID with precise positioning for high-sensitivity magnetization measurements. In the preliminary magnetization measurements of this device, we observed vortices trapped into the plate and thus the lower critical field. The improved magnetization measurement device developed to exclude undesirable flux intrusion successfully enabled high-sensitivity detection of quantized vortex. © 2016, Springer Science+Business Media New York.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kikugawa2016b,

title = {Interplanar coupling-dependent magnetoresistivity in high-purity layered metals},

author = {N Kikugawa and P Goswami and A Kiswandhi and E S Choi and D Graf and R E Baumbach and J S Brooks and K Sugii and Y Iida and M Nishio and S Uji and T Terashima and P M C Rourke and N E Hussey and H Takatsu and S Yonezawa and Y Maeno and L Balicas},

doi = {10.1038/ncomms10903},

year  = {2016},

date = {2016-01-01},

journal = {Nature Communications},

volume = {7},

abstract = {The magnetic field-induced changes in the conductivity of metals are the subject of intense interest, both for revealing new phenomena and as a valuable tool for determining their Fermi surface. Here we report a hitherto unobserved magnetoresistive effect in ultra-clean layered metals, namely a negative longitudinal magnetoresistance that is capable of overcoming their very pronounced orbital one. This effect is correlated with the interlayer coupling disappearing for fields applied along the so-called Yamaji angles where the interlayer coupling vanishes. Therefore, it is intrinsically associated with the Fermi points in the field-induced quasi-one-dimensional electronic dispersion, implying that it results from the axial anomaly among these Fermi points. In its original formulation, the anomaly is predicted to violate separate number conservation laws for left-and right-handed chiral (for example, Weyl) fermions. Its observation in PdCoO2, PtCoO2 and Sr2RuO4 suggests that the anomaly affects the transport of clean conductors, in particular near the quantum limit.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kittaka201681,

title = {First-order superconducting transition of Sr2RuO4 investigated by magnetization and magnetic torque},

author = {S Kittaka and A Kasahara and T Sakakibara and D Shibata and S Yonezawa and Y Maeno and K Tenya and K Machida},

doi = {10.1016/j.jmmm.2015.07.004},

year  = {2016},

date = {2016-01-01},

journal = {Journal of Magnetism and Magnetic Materials},

volume = {400},

pages = {81-83},

abstract = {The first-order superconducting transition, recently discovered in a long-standing candidate for a spin-triplet chiral-p-wave superconductor Sr2RuO4, is mysterious because it is not expected within the present scenario of spin-triplet superconductivity. To uncover its mechanism, we have measured the magnetization and the magnetic torque using an ultra-clean single crystal of Sr2RuO4 down to 0.1 K. In this study, the magnetic-field orientation has been controlled with a high precision within the accuracy of 0.01°. We observed a sharp magnetization jump of as large as 0.01 emu/g with a field hysteresis of 100 Oe at 0.1 K. With increasing temperature, this magnetization jump decreases and diminishes above 0.8 K. The magnetic torque indicates that the first-order transition occurs only when the magnetic field is applied close to the ab plane within 2 degrees deviation. These features of the first-order transition provide the keystone issues whose resolution is crucial in uncovering a "hidden" pair-breaking mechanism within the triplet-pairing scenario, or might urge the reconsideration of the order parameter in Sr2RuO4. © 2015 Elsevier B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}