論文リスト

@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.},

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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},

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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.},

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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.},

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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.},

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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.},

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pubstate = {published},

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}

@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.},

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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}

}

@article{Manago2016b,

title = {Absence of the O 17 Knight-shift changes across the first-order phase transition line in Sr2RuO4},

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

doi = {10.1103/PhysRevB.94.180507},

year  = {2016},

date = {2016-01-01},

journal = {Physical Review B},

volume = {94},

number = {18},

abstract = {We performed O17 nuclear magnetic resonance measurements on superconducting (SC) Sr2RuO4 under in-plane magnetic fields. We found that no new signal appears in the SC state and that the O17 Knight shifts obtained from the double-site measurements remain constant across the first-order phase-transition line, as well as across the second-order phase-transition line as already reported. The present results indicate that the SC spin susceptibility does not decrease in the high-field region, although a magnetization jump in the SC state was reported at low temperatures. Because the spin susceptibility is unchanged in the SC state in Sr2RuO4, we suggest that the first-order phase transition across the upper critical field should be interpreted as a depairing mechanism other than the conventional Pauli-paramagnetic effect. © 2016 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Chen2016,

title = {New Fluoride-arsenide Diluted Magnetic Semiconductor (Ba,K)F(Zn,Mn)As with Independent Spin and Charge Doping},

author = {B Chen and Z Deng and W Li and M Gao and Q Liu and C Z Gu and F X Hu and B G Shen and B Frandsen and S Cheung and L Lian and Y J Uemura and C Ding and S Guo and F Ning and T J S Munsie and M N Wilson and Y Cai and G Luke and Z Guguchia and S Yonezawa and Z Li and C Jin},

doi = {10.1038/srep36578},

year  = {2016},

date = {2016-01-01},

journal = {Scientific Reports},

volume = {6},

abstract = {We report the discovery of a new fluoride-arsenide bulk diluted magnetic semiconductor (Ba,K)F(Zn,Mn)As with the tetragonal ZrCuSiAs-type structure which is identical to that of the "1111" iron-based superconductors. The joint hole doping via (Ba,K) substitution &spin doping via (Zn,Mn) substitution results in ferromagnetic order with Curie temperature up to 30 K and demonstrates that the ferromagnetic interactions between the localized spins are mediated by the carriers. Muon spin relaxation measurements confirm the intrinsic nature of the long range magnetic order in the entire volume in the ferromagnetic phase. This is the first time that a diluted magnetic semiconductor with decoupled spin and charge doping is achieved in a fluoride compound. Comparing to the isostructure oxide counterpart of LaOZnSb, the fluoride DMS (Ba,K)F(Zn,Mn)As shows much improved semiconductive behavior that would be benefit for further application developments. © 2016 The Author(s).},

note = {cited By 12},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jerome2016357,

title = {Novel superconducting phenomena in quasi-one-dimensional Bechgaard salts},

author = {D Jerome and S Yonezawa},

doi = {10.1016/j.crhy.2015.12.003},

year  = {2016},

date = {2016-01-01},

journal = {Comptes Rendus Physique},

volume = {17},

number = {3-4},

pages = {357-375},

abstract = {It is the saturation of the transition temperature Tc in the range of 24 K for known materials in the late sixties that triggered the search for additional materials offering new coupling mechanisms leading in turn to higher Tc's. As a result of this stimulation, superconductivity in organic matter was discovered in tetramethyl-tetraselenafulvalene-hexafluorophosphate, (TMTSF)2PF6, in 1979, in the laboratory founded at Orsay by Professor Friedel and his colleagues in 1962. Although this conductor is a prototype example for low-dimensional physics, we mostly focus in this article on the superconducting phase of the ambient-pressure superconductor (TMTSF)2ClO4, which has been studied most intensively among the TMTSF salts. We shall present a series of experimental results supporting nodal d-wave symmetry for the superconducting gap in these prototypical quasi-one-dimensional conductors. © 2015 Académie des sciences.},

note = {cited By 9},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kasahara2016,

title = {Giant superconducting fluctuations in the compensated semimetal FeSe at the BCS-BEC crossover},

author = {S Kasahara and T Yamashita and A Shi and R Kobayashi and Y Shimoyama and T Watashige and K Ishida and T Terashima and T Wolf and F Hardy and C Meingast and H V Löhneysen and A Levchenko and T Shibauchi and Y Matsuda},

doi = {10.1038/ncomms12843},

year  = {2016},

date = {2016-01-01},

journal = {Nature Communications},

volume = {7},

abstract = {The physics of the crossover between weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein condensate (BEC) limits gives a unified framework of quantum-bound (superfluid) states of interacting fermions. This crossover has been studied in the ultracold atomic systems, but is extremely difficult to be realized for electrons in solids. Recently, the superconducting semimetal FeSe with a transition temperature Tc =8.5 K has been found to be deep inside the BCS-BEC crossover regime. Here we report experimental signatures of preformed Cooper pairing in FeSe, whose energy scale is comparable to the Fermi energies. In stark contrast to usual superconductors, large non-linear diamagnetism by far exceeding the standard Gaussian superconducting fluctuations is observed below T∗∼20 K, providing thermodynamic evidence for prevailing phase fluctuations of superconductivity. Nuclear magnetic resonance and transport data give evidence of pseudogap formation at ∼T∗. The multiband superconductivity along with electron-hole compensation in FeSe may highlight a novel aspect of the BCS-BEC crossover physics. © The Author(s) 2016.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kikugawa20155573,

title = {Single-Crystal Growth of a Perovskite Ruthenate SrRuO3 by the Floating-Zone Method},

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

doi = {10.1021/acs.cgd.5b01248},

year  = {2015},

date = {2015-01-01},

journal = {Crystal Growth and Design},

volume = {15},

number = {11},

pages = {5573-5577},

abstract = {We report single-crystal growth of a perovskite ruthenate SrRuO3 by the floating-zone method using an infrared image furnace. By employing a cold trap for the growth, we prevented the evaporated RuO2 from coating the inner surface of a quartz tube and were thereby able to maintain a stable molten zone during the growth. Powder X-ray and Laue diffraction measurements confirmed the quality of the grown single crystal. The crystal was cut into a 1.4 mm × 1.4 mm × 3.0 mm rectangle that was characterized by magnetic susceptibility, magnetization, and specific heat measurements. The crystal showed a ferromagnetic transition with a Curie temperature of 163.5 K, and the coercive field was as low as 0.004 T. The residual resistivity was 1.05 cm, corresponding to a residual resistivity ratio of 192. These results indicate that the grown crystal is high-quality. Electrical resistivity measurements show temperature-squared behavior, revealing that a Fermi-liquid-like electron-electron scattering is dominant. Together with a large electronic specific heat coefficient with 30 mJ K-2 mol-1, we confirm that the ferromagnetic SrRuO3 is a strongly correlated material. © 2015 American Chemical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida2015,

title = {Spin polarization enhanced by spin-triplet pairing in Sr2RuO4 probed by NMR},

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

doi = {10.1103/PhysRevB.92.100502},

year  = {2015},

date = {2015-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {92},

number = {10},

abstract = {We report a phenomenon intimately related to the spin-triplet superconductivity. It is well known that the spin susceptibility decreases below the superconducting transition temperature in almost all superconductors because of spin-singlet pair formation, while it may remain unchanged in a handful of spin-triplet exceptions. Here we report the observation in Sr2RuO4 with nuclear magnetic resonance that the spin susceptibility originating from the Ru-4d electron slightly increases by ∼2% of the total and becomes inhomogeneous in the superconducting state. These are reasonably explained if the electron pairs form the equal-spin pairing in the mixed state. A similar phenomenon was predicted for superfluid He340 years ago, but had never been demonstrated in any superconductor. © 2015 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Saitoh2015,

title = {Inversion symmetry of Josephson current as test of chiral domain wall motion in Sr2RuO4},

author = {K Saitoh and S Kashiwaya and H Kashiwaya and Y Mawatari and Y Asano and Y Tanaka and Y Maeno},

doi = {10.1103/PhysRevB.92.100504},

year  = {2015},

date = {2015-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {92},

number = {10},

abstract = {Clarifying the chiral domain structure of superconducting Sr2RuO4 has been a long-standing issue in identifying its peculiar topological superconducting state. We evaluated the critical current Ic versus the magnetic field H of Nb/Sr2RuO4 Josephson junctions, changing the junction dimension in expectation of that the number of domains in the junction is controlled. Ic(H) exhibits a recovery from inversion symmetry breaking to invariance when the dimension is reduced to several microns. This inversion invariant behavior indicates the disappearance of domain walls; thus, the size of a single domain is estimated at approximately several microns. © 2015 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yonezawa2015,

title = {Compact AC susceptometer for fast sample characterization down to 0.1 K},

author = {S Yonezawa and T Higuchi and Y Sugimoto and C Sow and Y Maeno},

doi = {10.1063/1.4929871},

year  = {2015},

date = {2015-01-01},

journal = {Review of Scientific Instruments},

volume = {86},

number = {9},

abstract = {We report a new design of an AC magnetic susceptometer compatible with the Physical Properties Measurement System (PPMS) by Quantum Design, as well as with its adiabatic demagnetization refrigerator option. With the elaborate compact design, the susceptometer allows simple and quick sample mounting process. The high performance of the susceptometer down to 0.1 K is demonstrated using several superconducting and magnetic materials. This susceptometer provides a method to quickly investigate qualities of a large number of samples in the wide temperature range between 0.1 and 300 K. © 2015 AIP Publishing LLC.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hicks2015,

title = {Quantum oscillations and magnetic reconstruction in the delafossite PdCrO2},

author = {C W Hicks and A S Gibbs and L Zhao and P Kushwaha and H Borrmann and A P Mackenzie and H Takatsu and S Yonezawa and Y Maeno and E A Yelland},

doi = {10.1103/PhysRevB.92.014425},

year  = {2015},

date = {2015-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {92},

number = {1},

abstract = {We report quantum oscillation data on the metallic triangular antiferromagnet PdCrO2. We find that, to very high accuracy, the observed frequencies of PdCrO2 can be reproduced by reconstruction of the (nonmagnetic) PdCoO2 Fermi surface into a reduced zone. The reduced zone corresponds to a magnetic cell containing six chromium sites, giving a 3×3 in-plane reconstruction, and ×2 interplane reconstruction. The interplane ordering represents a reduction in lattice symmetry, possibly to monoclinic, and an associated lattice distortion is expected. In addition, we report a magnetic transition under an applied in-plane field that is probably equivalent to the spin-flop transition reported for CuCrO2, and present data on its field-angle dependence. We also report measurements of the resistivity of PdCrO2 up to 500 K. © 2015 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Cortie2015,

title = {Spin fluctuations in the exotic metallic state of Sr2RuO4 studied with β-NMR},

author = {D L Cortie and T Buck and M H Dehn and R F Kiefl and C D P Levy and R M L McFadden and G D Morris and M R Pearson and Z Salman and Y Maeno and W A MacFarlane},

doi = {10.1103/PhysRevB.91.241113},

year  = {2015},

date = {2015-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {91},

number = {24},

abstract = {A β-NMR study was performed on a Sr2RuO4 crystal in the metallic state using a beam of spin-polarized 8Li+ implanted at a mean depth of 90 nm. The 8Li+ spin-lattice relaxation rate is strongly influenced by the onset of incommensurate spin fluctuations. The nuclear relaxation rate can be explained using previously published bulk 17O NMR and inelastic neutron spectroscopy measurements of the dynamic magnetic susceptibility to model the hyperfine coupling. A well-resolved quadrupolar-split NMR for 8Li+ implies a static stopping position in an interstitial site. The 8Li+ Knight shift is highly sensitive to the anisotropic static susceptibility. © 2015 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Shibata2015,

title = {Quenched metastable vortex states in Sr2RuO4},

author = {D Shibata and H Tanaka and S Yonezawa and T Nojima and Y Maeno},

doi = {10.1103/PhysRevB.91.104514},

year  = {2015},

date = {2015-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {91},

number = {10},

abstract = {Sr2RuO4, a leading-candidate spin-triplet superconductor and a highly anisotropic quasi-two-dimensional type II superconductor, provides a unique opportunity to study unconventional as well as conventional vortex phases. To investigate its vortex-matter phases, we studied the ac susceptibility of Sr2RuO4 for fields parallel to the RuO2 plane by adapting two different thermal processes: In addition to the ordinary field sweep (FS) process, we employed the "each-point field-cooling" (EPFC) process, in which the superconductivity is once thermally destroyed before collecting the data. We find that the ac susceptibility signal substantially changes with the EPFC process. This result indicates that we succeed in inducing new metastable vortex states via the EPFC process. We also find a new field scale H∗1, below which the FS and EPFC processes provide the same value of the ac susceptibility. This new field scale suggests a liquidlike vortex state in the low-field region. © 2015 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Grigera2015,

title = {An intermediate state between the kagome-ice and the fully polarized state in Dy 2 Ti 2 O 7},

author = {S A Grigera and R A Borzi and D G Slobinsky and A S Gibbs and R Higashinaka and Y Maeno and T S Grigera},

doi = {10.4279/PIP.070009},

year  = {2015},

date = {2015-01-01},

journal = {Papers in Physics},

volume = {7},

abstract = {Dy 2 Ti 2 O 7 is at present the cleanest example of a spin-ice material. Previous theoretical and experimental work on the first-order transition between the kagome-ice and the fully polarized state has been taken as a validation for the dipolar spin-ice model. Here we investigate in further depth this phase transition using ac-susceptibility and dc-magnetization, and compare this results with Monte-Carlo simulations and previous magnetization and specific heat measurements. We find signatures of an intermediate state between the kagome-ice and full polarization. This signatures are absent in current theoretical models used to describe spin-ice materials. © 2013, Instituto de Fisica de Liquidos y Sistemas Biologicos. All right reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Frandsen2015,

title = {Superconducting properties of noncentrosymmetric superconductor CaIrSi3 investigated by muon spin relaxation and rotation},

author = {B A Frandsen and S C Cheung and T Goko and L Liu and T Medina and T S J Munsie and G M Luke and P J Baker and M P Jimenez S. and G Eguchi and S Yonezawa and Y Maeno and Y J Uemura},

doi = {10.1103/PhysRevB.91.014511},

year  = {2015},

date = {2015-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {91},

number = {1},

abstract = {We have employed muon spin relaxation and rotation (μSR) to investigate the superconducting properties of the noncentrosymmetric superconductor CaIrSi3. Measurements of single-crystal specimens confirm the development of a robust superconducting state below Tc=3.55±0.1K with a ground-state magnetic penetration depth of λL=288±10nm and a coherence length of ξ=28.8±0.1nm. The temperature evolution of the superfluid density indicates a nodeless superconducting gap structure dominated by an isotropic spin-singlet component in the dirty limit with a carrier density of n=(4.6±0.2)×1022cm-3 as determined by Hall resistance measurements. We find no evidence of spontaneous time-reversal symmetry breaking in the superconducting state within an accuracy of 0.05 G. These observations suggest that the influence of any spin-triplet pairing component or multiple gap structure associated with noncentrosymmetric physics is very weak or entirely absent in CaIrSi3. © 2015 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Taniguchi2015,

title = {Higher-Tc superconducting phase in Sr2RuO4 induced by in-plane uniaxial pressure},

author = {H Taniguchi and K Nishimura and S K Goh and S Yonezawa and Y Maeno},

doi = {10.7566/JPSJ.84.014707},

year  = {2015},

date = {2015-01-01},

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

volume = {84},

number = {1},

abstract = {We revealed that the superconducting transition temperature Tc of the multi-component superconductor Sr2RuO4 is enhanced to 3.3K under in-plane uniaxial pressure that reduces the tetragonal crystal symmetry. This result suggests that new superconducting phases with a one-component order parameter are induced. We have also clarified the in-plane pressure direction dependence of the emergence of this higher-Tc superconducting phase: pressure along the [100] direction is more favorable than pressure along the [110] direction. This result is probably closely related to the direct shortening of the in-plane Ru-O bond length along the pressure direction and the approach of the γ Fermi surface to the van Hove singularity under P||[100]. © 2015 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Anwar2015,

title = {Erratum: Ferromagnetic SrRuO3 thin-film deposition on a spin-triplet superconductor Sr2RuO4 with a highly conducting interface (Appl. Phys. Express (2015) 8 (015502))},

author = {M S Anwar and Y Jae Shin and S Ran Lee and S Jin Kang and Y Sugimoto and S Yonezawa and T Won Noh and Y Maeno},

doi = {10.7567/APEX.8.019202},

year  = {2015},

date = {2015-01-01},

journal = {Applied Physics Express},

volume = {8},

number = {1},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Anwar2015b,

title = {Ferromagnetic SrRuO3 thin-film deposition on a spin-triplet superconductor Sr2RuO4 with a highly conducting interface},

author = {M S Anwar and Y Jae Shin and S Ran Lee and S Jin Kang and Y Sugimoto and S Yonezawa and T Won Noh and Y Maeno},

doi = {10.7567/APEX.8.015502},

year  = {2015},

date = {2015-01-01},

journal = {Applied Physics Express},

volume = {8},

number = {1},

abstract = {Ferromagnetic SrRuO3 thin films are deposited on the ab surface of single crystals of the spin-triplet superconductor (TSC) Sr2RuO4 as substrates using pulsed laser deposition. The films are under a severe in-plane compressive strain. Nevertheless, the films exhibit ferromagnetic order with the easy axis along the c-direction below the Curie temperature of 158 K. The electrical transport reveals that the SrRuO3/Sr2RuO4 interface is highly conducting, in contrast with the interface between other normal metals and the ab surface of Sr2RuO4. Our results stimulate investigations on proximity effects between a ferromagnet and a TSC. © 2015 The Japan Society of Applied Physics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yamanaka2015,

title = {Interface between heavy fermions and normal electrons investigated by spatially resolved nuclear magnetic resonance},

author = {T Yamanaka and M Shimozawa and R Endo and Y Mizukami and H Shishido and T Terashima and T Shibauchi and Y Matsuda and K Ishida},

doi = {10.1103/PhysRevB.92.241105},

year  = {2015},

date = {2015-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {92},

number = {24},

abstract = {We have studied the superlattices with alternating block layers (BLs) of heavy-fermion superconductor CeCoIn5 and conventional-metal YbCoIn5 by site-selective nuclear magnetic resonance spectroscopy, which uniquely offers spatially resolved dynamical magnetic information. We find that the presence of antiferromagnetic fluctuations is confined to the Ce BLs, indicating that magnetic degrees of freedom of felectrons are quenched inside the Yb BLs. Contrary to simple expectations that the two dimensionalization enhances fluctuations, we observe that antiferromagnetic fluctuations are rapidly suppressed with decreasing Ce BL thickness. Moreover, the suppression is more prominent near the interfaces between the BLs. These results imply significant effects of local inversion symmetry breaking at the interfaces. © 2015 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Manago2015,

title = {Effect of Geomagnetism on 101Ru Nuclear Quadrupole Resonance Measurements of CeRu2},

author = {M Manago and K Ishida and T D Matsuda and Y Onuki},

doi = {10.7566/JPSJ.84.115001},

year  = {2015},

date = {2015-01-01},

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

volume = {84},

number = {11},

abstract = {We performed 101Ru nuclear quadrupole resonance (NQR) measurements on the s-wave superconductor CeRu2 and found oscillatory behavior in the spin-echo amplitude at the |±1/2 虠 |±3/2 transitions but not at the |±3/2 虠 |±5/2 transitions. The modulation disappears in the superconducting state or in a magnetic shield, which implies a geomagnetic field effect. Our results indicate that the NQR spin-echo decay curve at the |±1/2 虠 |±3/2 transitions is sensitive to a weak magnetic field. © 2015 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitagawa2015,

title = {Suppression of nonmagnetic insulating state by application of pressure in mineral tetrahedrite Cu12Sb4S13},

author = {S Kitagawa and T Sekiya and S Araki and T C Kobayashi and K Ishida and T Kambe and T Kimura and N Nishimoto and K Kudo and M Nohara},

doi = {10.7566/JPSJ.84.093701},

year  = {2015},

date = {2015-01-01},

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

volume = {84},

number = {9},

abstract = {The mineral tetrahedrite Cu12Sb4S13 exhibits a first-order metal-insulator transition (MIT) at TMI = 85K and ambient pressure. We measured the 63Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. 63Cu-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pressure and disappears at ~1.0 GPa. Two other anomalies are observed in the resistivity measurements, and the pressure-temperature phase diagram of Cu12Sb4S13 is constructed. ©2015 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Iye2015,

title = {Emergence of orbital nematicity in the tetragonal phase of BaFe2(As1-xPx)2},

author = {T Iye and M -H Julien and H Mayaffre and M Horvatić and C Berthier and K Ishida and H Ikeda and S Kasahara and T Shibauchi and Y Matsuda},

doi = {10.7566/JPSJ.84.043705},

year  = {2015},

date = {2015-01-01},

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

volume = {84},

number = {4},

abstract = {We report on 75As-NMR measurements in single crystalline BaFe2(As0.96P0.04)2 for magnetic fields parallel to the orthorhombic [110]o and [100]o directions above the structural transition temperature TS ≃ 121 K. A large difference in the linewidth between the two field directions reveals in-plane anisotropy of the electric field gradient, even in the tetragonal phase. This provides microscopic evidence of population imbalance between As-4px and 4py orbitals, which reaches |nx - ny| /|nx + ny| ∼ 15% at T → TS and is a natural consequence of the orbital ordering of Fe-3dxz and dyz electrons. Surprisingly, this orbital polarization is found to be already static near room temperature, suggesting that it arises from the pinning of anisotropic orbital fluctuations by disorder. The effect is found to be stronger below ∼160 K, which coincides with the appearance of nematicity in previous torque and photoemission measurements. These results impose strong constraints on microscopic models of the nematic state. ©2015 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Karube2015,

title = {Ferromagnetic critical behavior in U(Co1-xFex)Al (0≤x≤0.02) studied by Co 59 nuclear quadrupole resonance measurements FERROMAGNETIC CRITICAL BEHAVIOR in U(Co ... K. KARUBE, T. HATTORI, K. ISHIDA, and N. KIMURA},

author = {K Karube and T Hattori and K Ishida and N Kimura},

doi = {10.1103/PhysRevB.91.075131},

year  = {2015},

date = {2015-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {91},

number = {7},

abstract = {In order to investigate physical properties around a ferromagnetic (FM) quantum transition point and a tricritical point (TCP) in the itinerant-electron metamagnetic compound UCoAl, we have performed the Co59 nuclear quadrupole resonance (NQR) measurement for the Fe-substituted U(Co1-xFex)Al(x=0,0.5,1,and2%) in zero external magnetic field. The Fe concentration dependence of Co59-NQR spectra at low temperatures indicates that the first-order FM transition occurs at least above x=1%. The magnetic fluctuations along the c axis detected by the nuclear spin-spin relaxation rate 1/T2 exhibit an anomaly at Tmax∼20K and enhance with increasing x. These results are in good agreement with theoretical predictions and indicate the presence of prominent critical fluctuations at the TCP in this system. © 2015 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Böhmer2015,

title = {Origin of the tetragonal-to-orthorhombic phase transition in FeSe: A combined thermodynamic and NMR study of nematicity},

author = {A E Böhmer and T Arai and F Hardy and T Hattori and T Iye and T Wolf and H V Löhneysen and K Ishida and C Meingast},

doi = {10.1103/PhysRevLett.114.027001},

year  = {2015},

date = {2015-01-01},

journal = {Physical Review Letters},

volume = {114},

number = {2},

abstract = {The nature of the tetragonal-to-orthorhombic structural transition at Ts≈90K in single crystalline FeSe is studied using shear-modulus, heat-capacity, magnetization, and nuclear magnetic resonance measurements. The transition is shown to be accompanied by a large shear-modulus softening, which is practically identical to that of underdoped Ba(Fe,Co)2As2, suggesting a very similar strength of the electron-lattice coupling. On the other hand, a spin-fluctuation contribution to the spin-lattice relaxation rate is only observed below Ts. This indicates that the structural, or "nematic," phase transition in FeSe is not driven by magnetic fluctuations. © 2015 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kittaka2014,

title = {Sharp magnetization jump at the first-order superconducting transition in Sr2 RuO4},

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 = {10.1103/PhysRevB.90.220502},

year  = {2014},

date = {2014-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {90},

number = {22},

abstract = {The magnetization and magnetic torque of a high-quality single crystal of Sr2RuO4 have been measured down to 0.1 K under precise control of the magnetic-field orientation. When the magnetic field is applied exactly parallel to the ab plane, a sharp magnetization jump 4πδM of (0.74±0.15) G at the upper critical field Hc2,ab∼15 kOe with a field hysteresis of 100 Oe is observed at low temperatures, evidencing a first-order superconducting-normal transition. A strong magnetic torque appearing when H is slightly tilted away from the ab plane confirms an intrinsic anisotropy Γ=ξa/ξc of as large as 60 even at 100 mK, in contrast with the observed Hc2 anisotropy of ∼20. The present results raise fundamental issues in both the existing spin-triplet and spin-singlet scenarios, providing, in turn, crucial hints toward the resolution of the superconducting nature of Sr2RuO4. © 2014 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tsuchiya2014,

title = {Magnetization of a mesoscopic superconducting Sr2RuO4plate on Micro-dc-SQUIDs},

author = {S Tsuchiya and M Matsuno and R Ishiguro and H Kashiwaya and S Kashiwaya and S Nomura and H Takayanagi and Y Maeno},

doi = {10.7566/JPSJ.83.094715},

year  = {2014},

date = {2014-01-01},

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

volume = {83},

number = {9},

abstract = {We report on the measurement of the magnetization of mesoscopic plates made of the chiral p-wave superconductor Sr2RuO4by using micro-dc-superconducting quantum interference devices (SQUIDs) positioned immediately below the plates. The high sensitivity of the micro-dc-SQUIDs is expected to enable the detection of direction of the chirality. We measured the magnetization of mesoscopic Sr2RuO4plate-like crystals and found residual magnetization at the zero external field in the thin sample and detected a first critical field Hc1symmetric against the magnetic field direction. The observed symmetric first critical field Hc1is consistent with the formation of multi-chiral domain structures. We carefully discuss the origin of the residual magnetization and conclude that it is due to the remnant vortices rather than the chiral edge current. © 2014 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yonezawa2014,

title = {Specific-heat evidence of the first-order superconducting transition in Sr2RuO4},

author = {S Yonezawa and T Kajikawa and Y Maeno},

doi = {10.7566/JPSJ.83.083706},

year  = {2014},

date = {2014-01-01},

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

volume = {83},

number = {8},

abstract = {We investigate the specific heat of ultra pure single crystals of Sr2RuO4, a leading candidate spin-triplet superconductor. For the fi rst time, we obtained specific-heat evidence of the first-order superconducting transition below 0.8 K, namely, divergent-like peaks and clear hysteresis in the specific heat at the upper critical field. The first-order occurs for all in-plane field directions. The specific-heat features for the first-order transition are found to be sensitive to sample quality; in particular, the hysteresis totally disappears in a sample with slightly lower quality. These thermodynamic observations provide crucial bases for understanding the unconventional pair-breaking effect responsible for the first-order transition. © 2014 The Physical Society of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Takatsu2014,

title = {Magnetic structure of the conductive triangular-lattice antiferromagnet PdCrO 2},

author = {H Takatsu and G Nénert and H Kadowaki and H Yoshizawa and M Enderle and S Yonezawa and Y Maeno and J Kim and N Tsuji and M Takata and Y Zhao and M Green and C Broholm},

doi = {10.1103/PhysRevB.89.104408},

year  = {2014},

date = {2014-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {89},

number = {10},

abstract = {We performed neutron single-crystal and synchrotron x-ray powder diffraction experiments in order to investigate the magnetic and crystal structures of the conductive layered triangular-lattice antiferromagnet PdCrO2 with a putative spin chirality, which contributes to an unconventional anomalous Hall effect. We revealed that the ground-state magnetic structure is a commensurate and nearly coplanar 120â̂̃ spin structure. The 120â̂̃ planes in different Cr layers seem to tilt with one another, leading to a small noncoplanarity. Such a small but finite noncoplanar stacking of the 120â̂̃ planes gives rise to a finite scalar spin chirality, which may be responsible for the unconventional nature of the Hall effect of PdCrO2. © 2014 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ueno2014,

title = {Effective thickness of two-dimensional superconductivity in a tunable triangular quantum well of SrTiO3},

author = {K Ueno and T Nojima and S Yonezawa and M Kawasaki and Y Iwasa and Y Maeno},

doi = {10.1103/PhysRevB.89.020508},

year  = {2014},

date = {2014-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {89},

number = {2},

abstract = {We report two-dimensionality and effective thickness of the superconductivity of a SrTiO3 single-crystal surface induced by electric double-layer gating. The carrier density was tuned from 3 × 1013 to 1.1 × 1014 cm-2 by gating, where superconductivity appears with Tc of around 0.4 K. Typical two-dimensional behavior perfectly described by the Ginzburg-Landau equation was observed in the angular and temperature dependence of the upper critical magnetic field. The effective thickness of the superconducting layer remains nearly invariant, ranging from 11 to 13 nm, with increasing charge carrier density. This invariance contradicts the expected reduction in the thickness of the accumulation layer in a triangular quantum well model. This unexpected invariance of the superconducting layer thickness is probably a unique nature for a two-dimensional electron system in the incipient ferroelectric SrTiO 3. © 2014 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}