論文リスト

@article{CaSb2ARPES,

title = {Fermiology of a topological line-nodal compound  CaSb2  and its implication to superconductivity: Angle-resolved photoemission study},

author = {C-Wen Chuang and S Souma and A Moriya and K Nakayama and A Ikeda and M Kawaguchi and K Obata and S Ranjan Saha and H Takahashi and S Kitagawa and K Ishida and K Tanaka and M Kitamura and K Horiba and H Kumigashira and T Takahashi and S Yonezawa and J Paglione and Y Maeno and T Sato},

doi = {10.1103/PhysRevMaterials.6.104203},

year  = {2022},

date = {2022-10-24},

urldate = {2022-10-24},

journal = {Physical Review Materials},

volume = {6},

issue = {10},

pages = {104203},

abstract = {We performed angle-resolved photoemission spectroscopy with microfocused beam on a topological line-nodal compound CaSb2 which undergoes a superconducting transition at the onset Tc ∼ 1.8 K, to clarify the Fermi-surface topology relevant to the occurrence of superconductivity. We found that a three-dimensional hole pocket at the Γ point is commonly seen for two types of single-crystalline samples fabricated by different growth conditions. On the other hand, the carrier-doping level estimated from the position of the chemical potential was found to be sensitive to the sample fabrication condition. The cylindrical electron pocket at the Y(C) point predicted by the calculations is absent in one of the two samples, despite the fact that both samples commonly show superconductivity with similar Tc's. This suggests a key role of the three-dimensional hole pocket to the occurrence of superconductivity, and further points to an intriguing possibility to control the topological nature of superconductivity by carrier tuning in CaSb2.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{M.Manago_JPSJ_2022,

title = {Site Split of Antiferromagnetic α-Mn Revealed by 55Mn Nuclear Magnetic Resonance},

author = {M Manago and G Motoyama and S Nishigori and K Fujiwara and K Kinjo and S Kitagawa and K Ishida and K Akiba and S Araki and T C Kobayashi and Hisatomo Harima},

url = {https://arxiv.org/abs/2210.02754},

doi = {10.7566/JPSJ.91.113701},

year  = {2022},

date = {2022-10-06},

urldate = {2022-10-06},

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

volume = {91},

issue = {11},

pages = {113701},

abstract = {The magnetic structure of antiferromagnetic α-Mn has been unclarified for almost 70 years since its magnetism was discovered. We measured the zero-field nuclear magnetic resonance spectra of antiferromagnetic α-Mn to obtain further insight into magnetism below TN = 95 K. The site II spectra split into two sites with five subpeaks owing to quadrupole interaction, and this shows that the ordered moments at site II are slightly tilted from the [001] direction. The site III spectra revealed that this site splits into four sites below TN. These findings clearly demonstrate that the antiferromagnetic α-Mn symmetry is lower than previously considered.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{S.Kitagawa_PRB_2022,

title = {Enhancement of charge-neutral fermionic excitations near the spin-flop transition in the magnetic Kondo material YbIr3Si7},

author = {S Kitagawa and T Kobayashi and F Hori and K Ishida and A H Nevidomskyy and L Qian and E Morosan},

url = {https://doi.org/10.1103/PhysRevB.106.L100405

https://arxiv.org/abs/2209.10844},

doi = {10.1103/PhysRevB.106.L100405},

year  = {2022},

date = {2022-09-16},

urldate = {2022-09-16},

journal = {Physical Review B},

volume = {106},

pages = {L100405},

abstract = {The new Kondo material YbIr3Si7, similar to other Kondo insulators, has been reported to exhibit charge-neutral fermionic excitations through measurements of specific heat and thermal conductivity at low temperatures. 

We performed 29Si−NMR on YbIr3Si7 to investigate the magnetic response of charge-neutral fermions from a microscopic perspective. In low magnetic fields parallel to the c axis, a single NMR peak in the paramagnetic state splits into three peaks below TN. 

In contrast, only a slight shift of the single NMR peak was observed in high magnetic fields. This spectral change as a function of the c

-axis magnetic field is interpreted as a spin-flop transition, at which the magnetic moments oriented along the c axis antiferromagnetic (AFM-I) phase are rotated to the ab plane with a ferromagnetic component along the c-axis (AFM-II phase). In the vicinity of the spin-flop magnetic field 

HM, the nuclear spin-lattice relaxation rate 1/T1 was found to be proportional to temperature at low temperatures, indicating the existence of charge-neutral fermions. Furthermore, a peak of 1/T1 versus the c-axis magnetic field suggests that the charge-neutral fermions in YbIr3Si7 are closely related to its magnetic properties. Our findings shed light on the origin of charge-neutral fermions in insulators.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{A.Ikeda_PRB_2022,

title = {Quasi-two-dimensional Fermi surface of superconducting line-nodal metal  CaSb2},

author = {A Ikeda and S Ranjan Saha and D Graf and P Saraf and D Sergeevich Sokratov and Y Hu and H Takahashi and S Yamane and A Jayaraj and J Sławińska and M Buongiorno Nardelli and S Yonezawa and Y Maeno and J Paglione},

url = {https://arxiv.org/abs/2206.15346},

doi = {10.1103/PhysRevB.106.075151},

year  = {2022},

date = {2022-08-29},

urldate = {2022-08-29},

journal = {Physical Review B},

volume = {106},

issue = {7},

pages = {075151},

abstract = {We report on the Fermi surfaces and superconducting parameters of CaSb2 single crystals (superconducting below Tc ∼ 1.8 K) grown by the self-flux method. The frequency of de Haas–van Alphen and Shubnikov–de Haas oscillations evidences a quasi-two-dimensional (quasi-2D) Fermi surface, consistent with one of the Fermi surfaces forming Dirac lines predicted by first-principles calculations. Measurements in the superconducting state reveal that CaSb2 is close to a type-I superconductor with the Ginzburg-Landau parameter of around unity. The temperature dependence of the upper critical field Hc2 is well described by a model considering two superconducting bands, and the enhancement of the effective mass estimated from Hc2 (0 K) is consistent with the quasi-2D band observed by the quantum oscillations. Our results indicate that a quasi-2D band forming Dirac lines contributes to the superconductivity in CaSb2.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{K.Kinjo_Science_2022,

title = {Superconducting spin smecticity evidencing the Fulde-Ferrell-Larkin-Ovchinnikov state in Sr2RuO4},

author = {K Kinjo and M Manago and S Kitagawa and Z Q Mao and S Yonezawa and Y Maeno and K. Ishida},

url = {https://www.science.org/doi/10.1126/science.abb0332},

doi = {10.1126/science.abb0332},

year  = {2022},

date = {2022-04-21},

journal = {Science},

volume = {376},

issue = {6591},

pages = {397-400},

abstract = {Translational symmetry breaking is antagonistic to static fluidity but can be realized in superconductors, which host a quantum-mechanical coherent fluid formed by electron pairs. A peculiar example of such a state is the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, induced by a time-reversal symmetry–breaking magnetic field applied to spin-singlet superconductors. This state is intrinsically accompanied by the superconducting spin smecticity, spin density–modulated fluidity with spontaneous translational-symmetry breaking. Detection of such spin smecticity provides unambiguous evidence for the FFLO state, but its observation has been challenging. Here, we report the characteristic “double-horn” nuclear magnetic resonance spectrum in the layered superconductor Sr2RuO4 near its upper critical field, indicating the spatial sinusoidal modulation of spin density that is consistent with superconducting spin smecticity. Our work reveals that Sr2RuO4 provides a versatile platform for studying FFLO physics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{K.Kinjo_PRB_2022,

title = {Drastic change in magnetic anisotropy of UTe2 under pressure revealed by 125Te -NMR},

author = {K Kinjo and H Fujibayashi and G Nakamine and S Kitagawa and K Ishida and Y Tokunaga and H Sakai and S Kambe and A Nakamura and Y Shimizu and Y Homma and D Li and F Honda and D Aoki},

url = {https://arxiv.org/abs/2203.12934},

doi = {10.1103/PhysRevB.105.L140502},

year  = {2022},

date = {2022-04-06},

urldate = {2022-04-06},

journal = {Physical Review B},

volume = {105},

issue = {14},

pages = {L140502},

abstract = {To investigate the normal-state magnetic properties of UTe2 under pressure, we perform 125Te nuclear magnetic resonance (NMR) measurements up to 2 GPa. Below 1.2 GPa, the b-axis NMR Knight shift shows a broad maximum at the so-called T_chimax on cooling, which is consistent with the magnetization measurement under pressure. T_chimax decreases with increasing pressure and disappears at the critical pressure Pc = 1.7 GPa, above which superconductivity is destroyed. This tendency is also observed in the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1. At low pressures, 1/T1 shows a conventional Fermi-liquid behavior (1/T1T = constant) at low temperatures, indicating the formation of the heavy-fermion state. Above Pc, 1/T1T follows a 1/T behavior without any crossover to the heavy-fermion state down to the lowest temperature (~3 K). In addition, the NMR signals disappear below 3 K, due to the influence of the magnetically ordered moments. From the pressure dependence of the T_chimax and Knight shift, it was found that the Fermi surface character is abruptly changed at Pc, and that superconductivity is observed only in the heavy-fermion state.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{uchida2022high,

title = {High-order harmonic generation and its unconventional scaling law in the Mott-insulating Ca_{2}RuO_{4}},

author = {K Uchida and G Mattoni and S Yonezawa and F Nakamura and Y Maeno and K Tanaka},

url = {https://arxiv.org/abs/2106.15478},

doi = {10.1103/PhysRevLett.128.127401},

year  = {2022},

date = {2022-03-23},

urldate = {2022-03-23},

journal = {Physical Review Letters},

volume = {128},

number = {127401},

abstract = {Competition and cooperation among orders is at the heart of many-body physics in strongly correlated materials and leads to their rich physical properties. It is crucial to investigate what impact many-body physics has on extreme nonlinear optical phenomena, with the possibility of controlling material properties by light. However, the effect of competing orders and electron-electron correlations on highly nonlinear optical phenomena has not yet been experimentally clarified. Here, we investigated high-order harmonic generation from the Mott-insulating phase of Ca2RuO4. Changing the gap energy in Ca2RuO4 as a function of temperature, we observed a strong enhancement of high order harmonic generation at 50 K, increasing up to several hundred times compared to room temperature. We discovered that this enhancement can be well reproduced by an empirical scaling law that depends only on the material gap energy and photon emission energy. Such a scaling law can hardly be explained by the electronic structure change in the single particle model and has not been predicted by previous theoretical studies on HHG in the simple Mott-Hubbard model. Our results suggest that the highly nonlinear optical response of strongly correlated materials is influenced by competition among the multiple degrees of freedom and electron-electron correlations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{H.Fujibayashi_JPSJ_2022,

title = {Superconducting Order Parameter in UTe2 Determined by Knight Shift Measurement},

author = {H Fujibayashi and G Nakamine and K Kinjo and S Kitagawa and K Ishida and Y Tokunaga and H Sakai and S Kambe and A Nakamura and Y Shimizu and Y Homma and D Li and F Honda and D Aoki},

url = {https://doi.org/10.7566/JPSJ.91.043705

https://arxiv.org/abs/2203.08598},

doi = {10.7566/JPSJ.91.043705},

year  = {2022},

date = {2022-03-11},

urldate = {2022-03-11},

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

volume = {91},

number = {04},

pages = {043705},

abstract = {This study investigates the spin susceptibility in U-based superconductor UTe2 in the superconducting (SC) state by using Knight shift measurements for a magnetic field H along the a axis, which is the magnetic easy axis of UTe2. 

Although a tiny anomaly ascribed to the SC diamagnetic effect was observed just below the SC transition temperature Tc, the a-axis Knight shift in the SC state shows no significant decrease, following the extrapolation from the normal-state temperature dependence. 

This indicates that the spin susceptibility is nearly unchanged below Tc. 

Considering the previous Knight shift results for H∥b and H∥c, the dominant SC state is determined to be B3u in the spin-triplet pairing, which is consistent with the spin anisotropy in the normal state. 

The present result shows that UTe2 is a spin-triplet superconductor with spin degrees of freedom.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{S.Kitagawa_JPSJ_2021,

title = {Two-Dimensional XY-Type Magnetic Properties of Locally Noncentrosymmetric Superconductor CeRh2As2},

author = {S Kitagawa and M Kibune and K Kinjo and M Manago and T Taniguchi and K Ishida and M Brando and E Hassinger and C Geibel and S Khim},

url = {https://doi.org/10.7566/JPSJ.91.043702

https://arxiv.org/abs/2203.03184},

doi = {10.7566/JPSJ.91.043702},

year  = {2022},

date = {2022-03-04},

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

volume = {91},

number = {04},

pages = {043702},

abstract = {We performed 75As-NMR measurements to investigate the normal-state magnetic properties of CeRh2As2, a recently-discovered heavy-fermion superconductor. 

The magnitude and temperature dependence of the Knight shift at the As(2) site indicate easy-plane-type magnetic anisotropy in CeRh2As2. 

With regard to spin fluctuations, the temperature dependence of the nuclear spin-lattice relaxation rate 1/T1 arising from the 4f electrons decreases from high-temperature constant behavior on cooling at ∼ 40~K, which is typical behavior of heavy-fermion systems. 

In addition, 1/T1 becomes constant at low temperatures, suggesting spatially two-dimensional antiferromagnetic fluctuations. Two-dimensional magnetic correlations in the real space are quite rare among heavy-fermion superconductors, and they may be a key factor in the unique superconducting multi-phase in CeRh2As2.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{S.Kitagawa_PRL_2022,

title = {Observation of Antiferromagnetic Order as Odd-Parity Multipoles inside the Superconducting Phase in  CeRh2As2},

author = {M Kibune and S Kitagawa and K Kinjo and S Ogata and M Manago and T Taniguchi and K Ishida and M Brando and E Hassinger and H Rosner and C Geibel and S Khim},

url = {https://arxiv.org/abs/2112.07081},

doi = {10.1103/PhysRevLett.128.057002},

year  = {2022},

date = {2022-02-03},

urldate = {2022-02-03},

journal = {Physical Review Letters},

volume = {128},

number = {05},

pages = {057002},

abstract = {Spatial inversion symmetry in crystal structures is closely related to the superconducting (SC) and magnetic properties of materials. Recently, several theoretical proposals that predict various interesting phenomena caused by the breaking of the local inversion symmetry have been presented. However, experimental validation has not yet progressed owing to the lack of model materials. Here we present evidence for antiferromagnetic (AFM) order in CeRh2As2 (SC transition temperature TSC ∼ 0.37 K ), wherein the Ce site breaks the local inversion symmetry. The evidence is based on the observation of different extents of broadening of the nuclear quadrupole resonance spectrum at two crystallographically inequivalent As sites. This AFM ordering breaks the inversion symmetry of this system, resulting in the activation of an odd-parity magnetic multipole. Moreover, the onset of antiferromagnetism TN within an SC phase, with TN < TSC , is quite unusual in systems wherein superconductivity coexists or competes with magnetism. Our observations show that CeRh2As2 is a promising system to study how the absence of local inversion symmetry induces or influences unconventional magnetic and SC states, as well as their interaction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Y.Tokunaga_JPSJ_2022,

title = {Slow Electronic Dynamics in the Paramagnetic State of UTe2},

author = {Y Tokunaga and H Sakai and S Kambe and Y Haga and Y Tokiwa and P Opletal and H Fujibayashi and K Kinjo and S Kitagawa and K Ishida and A Nakamura and Y Shimizu and Y Homma and D Li and F Honda and D Aoki},

url = {https://arxiv.org/abs/2201.07455},

doi = {10.7566/JPSJ.91.023707},

year  = {2022},

date = {2022-01-27},

urldate = {2022-01-27},

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

volume = {91},

issue = {02},

pages = {023707},

abstract = {125Te NMR experiments in field (H) applied along the easy magnetization axis (the a-axis) revealed slow electronic dynamics developing in the paramagnetic state of UTe2. The observed slow fluctuations are concerned with a successive growth of long-range electronic correlations below 30–40 K, where the spin susceptibility along the hard magnetization axis (the b-axis) shows a broad maximum. The experiments also imply that tiny amounts of disorder or defects locally disturb the long-range electronic correlations and develop an inhomogeneous electronic state at low temperatures, leading to a low temperature upturn observed in the bulk-susceptibility in H || a. We suggest that UTe2 would be located on the paramagnetic side near an electronic phase boundary, where either magnetic or Fermi-surface instability would be the origin of the characteristic fluctuations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Y.Sato_NComm_2022,

title = {Charge neutral fermions and magnetic field driven instability in insulating YbIr3Si7},

author = {Y Sato and S Suetsugu and T Tominaga and Y Kasahara and S Kasahara and T Kobayashi and S Kitagawa and K Ishida and R Peters and T Shibauchi and A H Nevidomskyy and L Qian and J M Moya and E Morosan and Y Matsuda},

url = {https://arxiv.org/abs/2103.13718},

doi = {10.1038/s41467-021-27541-9},

year  = {2022},

date = {2022-01-19},

urldate = {2022-01-19},

journal = {Nature Communications},

volume = {13},

pages = {394},

abstract = {Kondo lattice materials, where localized magnetic moments couple to itinerant electrons, provide a very rich backdrop for strong electron correlations. They are known to realize many exotic phenomena, with a dramatic example being recent observations of quantum oscillations and metallic thermal conduction in insulators, implying the emergence of enigmatic charge-neutral fermions. Here, we show that thermal conductivity and specific heat measurements in insulating YbIr3Si7 reveal emergent neutral excitations, whose properties are sensitively changed by a field-driven transition between two antiferromagnetic phases. In the low-field phase, a significant violation of the Wiedemann-Franz law demonstrates that YbIr3Si7 is a charge insulator but a thermal metal. In the high-field phase, thermal conductivity exhibits a sharp drop below 300 mK, indicating a transition from a thermal metal into an insulator/semimetal driven by the magnetic transition. These results suggest that spin degrees of freedom directly couple to the neutral fermions, whose emergent Fermi surface undergoes a field-driven instability at low temperatures.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nipponium,

title = {Ogawa’s nipponium and its re-assignment to rhenium},

author = {Y Hisamatsu and K Egashira and Y Maeno },

doi = {10.1007/s10698-021-09410-x},

year  = {2021},

date = {2021-10-18},

urldate = {2021-10-18},

journal = {Foundations of Chemistry},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{K.Ishida_PRB_2021,

title = {Pairing interaction in superconducting UCoGe tunable by magnetic field},

author = {K Ishida and S Matsuzaki and M Manago and T Hattori and S Kitagawa and M Hirata and T Sasaki and D Aoki},

url = {https://arxiv.org/abs/2109.14426},

doi = {10.1103/PhysRevB.104.144505},

year  = {2021},

date = {2021-10-18},

journal = {Physical Review B},

volume = {104},

number = {14},

pages = {144505},

abstract = {The mechanism of unconventional superconductivity, such as high-temperature-cuprate, Fe-based, and heavy-fermion superconductors, has been studied as a central issue in condensed-matter physics. Spin fluctuations, instead of phonons, are considered to be responsible for the formation of Cooper pairs, and many efforts have been made to confirm this mechanism experimentally. Although a qualitative consensus seems to have been obtained, experimental confirmation has not yet been achieved. This is owing to a lack of the quantitative comparison between theory and experiments. Here, we show a semiquantitative comparison between the superconducting-transition temperature ( T SC ) and spin fluctuations derived from the NMR experiment on the ferromagnetic (FM) superconductor UCoGe in which the FM fluctuations and superconductivity are tunable by external fields. The enhancement and abrupt suppression of T SC by applied fields, as well as the pressure variation of T SC around the FM criticality are well understood by the change in the FM fluctuations on the basis of the single-band spin-triplet theoretical formalism. The present comparisons strongly support the theoretical formalism of spin-fluctuation-mediated superconductivity, particularly in UCoGe.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{S.Kitagawa_PRB_2021,

title = {Peak in the superconducting transition temperature of the nonmagnetic topological line-nodal material CaSb_{2} under pressure},

author = {S Kitagawa and K Ishida and A Ikeda and M Kawaguchi and S Yonezawa and Y Maeno},

url = {https://arxiv.org/abs/2108.08992},

doi = {10.1103/PhysRevB.104.L060504},

year  = {2021},

date = {2021-08-17},

journal = {Physical Review B},

volume = {104},

number = {6},

pages = {L060504},

abstract = {Investigating the pressure dependence of the superconducting (SC) transition temperature Tc is crucial for understanding the SC mechanism. 

Herein, we report on the pressure dependence of Tc in the nonmagnetic topological line-nodal material CaSb2 based on measurements of electric resistance and alternating current magnetic susceptibility. 

Tc initially increases with increasing pressure and peaks at ~ 3.1 GPa. With a further increase in pressure, Tc decreases and finally becomes undetectable at 5.9 GPa. 

Because no signs of phase transition or Lifshitz transition are observed in the normal state, the peculiar peak structure of Tc suggests that CaSb2 has an unconventional SC character.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{V.Grinenko_ncomm,

title = {Unsplit superconducting and time reversal symmetry breaking transitions in Sr2RuO4 under hydrostatic pressure and disorder},

author = {V Grinenko and D Das and R Gupta and B Zinkl and N Kikugawa and Y Maeno and C W Hicks and H -H Klauss and M Sigrist and R Khasanov},

url = {https://arxiv.org/abs/2103.03600},

doi = {10.1038/s41467-021-24176-8},

year  = {2021},

date = {2021-06-24},

urldate = {2021-06-24},

journal = {Nature communications},

volume = {12},

pages = {3920},

abstract = {There is considerable evidence that the superconducting state of Sr2RuO4 breaks time reversal symmetry. In the experiments showing time reversal symmetry breaking, its onset temperature, TTRSB, is generally found to match the critical temperature, Tc, within resolution. In combination with evidence for even parity, this result has led to consideration of a dxz ± idyz order parameter. The degeneracy of the two components of this order parameter is protected by symmetry, yielding TTRSB = Tc, but it has a hard-to-explain horizontal line node at kz = 0. Therefore, s ± id and d ± ig order parameters are also under consideration. These avoid the horizontal line node, but require tuning to obtain TTRSB ≈ Tc. To obtain evidence distinguishing these two possible scenarios (of symmetry-protected versus accidental degeneracy), we employ zero-field muon spin rotation/relaxation to study pure Sr2RuO4 under hydrostatic pressure, and Sr1.98La0.02RuO4 at zero pressure. Both hydrostatic pressure and La substitution alter Tc without lifting the tetragonal lattice symmetry, so if the degeneracy is symmetry-protected, TTRSB should track changes in Tc, while if it is accidental, these transition temperatures should generally separate. We observe TTRSB to track Tc, supporting the hypothesis of dxz ± idyz order.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{PhysRevB.103.235147,

title = {Orbital dichotomy of Fermi liquid properties in  Sr2RuO4  revealed by Raman spectroscopy},

author = {J -C Philippe and B Baptiste and C Sow and Y Maeno and A Forget and D Colson and M Cazayous and A Sacuto and Y Gallais},

doi = {10.1103/PhysRevB.103.235147},

year  = {2021},

date = {2021-06-23},

urldate = {2021-06-23},

journal = {Physical Review B},

volume = {103},

number = {23},

pages = {235147},

abstract = {We report a polarization-resolved Raman spectroscopy study of the orbital dependence of the quasiparticle properties in the prototypical multiband Fermi liquid 

Sr2RuO4. We show that the quasiparticle scattering rate displays ω2 dependence, as expected for a Fermi liquid. In addition, we observe a clear polarization dependence in the energy and temperature dependence of the quasiparticle scattering rate and mass, with the dxz/yz orbital derived quasiparticles showing significantly more robust Fermi liquid properties than the dxy orbital derived ones. The observed orbital dichotomy of the quasiparticles is consistent with the picture of Sr2RuO4 as a Hund's metal. Our study establishes Raman scattering as a powerful probe of Fermi liquid properties in correlated metals.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{H.Takahashi_JPSJ_2021,

title = {S-Wave Superconductivity in the Dirac Line-Nodal Material CaSb2},

author = {H Takahashi and S Kitagawa and K Ishida and M Kawaguchi and A Ikeda and S Yonezawa and Y Maeno},

url = {https://arxiv.org/abs/2105.13614},

doi = {10.7566/JPSJ.90.073702},

year  = {2021},

date = {2021-06-11},

urldate = {2021-06-11},

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

volume = {90},

pages = {073702},

abstract = {We performed 121/123Sb-nuclear quadrupole resonance (NQR) measurements on the superconducting (SC) line-nodal material CaSb2 in order to investigate electronic properties in the normal and SC states from a microscopic point of view. In the normal state, the nuclear spin–lattice relaxation rate 1/T1 for the Sb(1) site, which is responsible for the line-nodal parts, is approximately proportional to temperature, indicating the conventional Fermi liquid state. From comparison with band structure calculations, it is considered that the NQR properties related to the line-nodal character are hidden because the conventional behavior originating from Fermi-surface parts away from the nodes is dominant. In the SC state, a clear coherence peak just below the transition temperature and an exponential decrease at lower temperatures were observed in 1/T1. These results strongly suggest that conventional s-wave superconductivity with a full gap is realized in CaSb2.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{G.Nakamine_JPSJ_2021,

title = {Inhomogeneous Superconducting State Probed by 125Te NMR on UTe2},

author = {G Nakamine and K Kinjo and S Kitagawa and K Ishida and Y Tokunaga and H Sakai and S Kambe and A Nakamura and Y Shimizu and Y Homma and D Li and F Honda and D Aoki},

url = {https://arxiv.org/abs/2105.11823},

doi = {10.7566/JPSJ.90.064709},

year  = {2021},

date = {2021-05-25},

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

volume = {90},

number = {064709},

pages = {7},

abstract = {UTe2 is a recently discovered promising candidate for a spin-triplet superconductor. In contrast to conventional spin-singlet superconductivity, spin-triplet superconductivity possesses spin and angular momentum degrees of freedom. To detect these degrees of freedom and obtain the solid evidence of spin-triplet superconductivity in UTe2, we have performed 125Te-NMR measurements, which are sensitive to the local spin susceptibility at a nuclear site. We previously reported that the shoulder signal appears in NMR spectra below the superconducting (SC) transition temperature Tc in H || b, and a slight decrease in the Knight shift along the b and c axes (Kb and Kc, respectively) below Tc at a low magnetic field H. Although the decrease in Kc vanished above 5.5 T, the decrease in Kb was independent of H up to 6.5 T. To clarify the origin of the shoulder signal and the trace of the decrease in Kb, we compared the 125Te-NMR spectra obtained when H || b and H || c and measured the 125Te-NMR spectra for H || b up to 14.5 T. The intensity of the shoulder signal observed for H || b has a maximum at ∼6 T and vanishes above 10 T, although the superconductivity is confirmed by the χAC measurements, which can survive up to 14.5 T (maximum H in the present measurement). Moreover, the decrease in Kb in the SC state starts to be small around 7 T and almost zero at 12.5 T. This indicates that the SC spin state gradually changes with the application of H. Meanwhile, in H || c, an unexpected broadening without the shoulder signals was observed below Tc at 1 T, and this broadening was quickly suppressed with increasing H. We construct the H–T phase diagram for H || b and H || c based on the NMR measurements and discuss possible SC states with the theoretical consideration. We suggest that the inhomogeneous SC state characterized by the broadening of the NMR spectrum originates from the spin degrees of freedom.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{K.Jenni_PRB2021,

title = {Neutron scattering studies on spin fluctuations in  Sr2RuO4},

author = {K Jenni and S Kunkemöller and P. Steffens and Y Sidis and R Bewley and Z Q Mao and Y Maeno and M Braden},

doi = {10.1103/PhysRevB.103.104511},

year  = {2021},

date = {2021-03-18},

urldate = {2021-03-18},

journal = {Physical Review B},

volume = {103},

number = {10},

pages = {104511},

abstract = {The magnetic excitations in Sr2RuO4 are studied by polarized and unpolarized neutron scattering experiments as a function of temperature. At the scattering vector of the Fermi-surface nesting with a half-integer out-of-plane component, there is no evidence for the appearance of a resonance excitation in the superconducting phase. The body of existing data indicates weakening of the scattered intensity in the nesting spectrum to occur at very low energies. The nesting signal persists up to 290 K but is strongly reduced. In contrast, a quasiferromagnetic contribution maintains its strength and still exhibits a finite width in momentum space.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{G.Nakamine_PRB_2021,

title = {Anisotropic response of spin susceptibility in the superconducting state of  UTe2  probed with  125Te − NMR  measurement},

author = {G Nakamine and K Kinjo and S Kitagawa and K Ishida and Y Tokunaga and H Sakai and S Kambe and A Nakamura and Y Shimizu and Y Homma and D Li and F Honda and D Aoki},

url = {https://arxiv.org/abs/2103.02876},

doi = {10.1103/PhysRevB.103.L100503},

year  = {2021},

date = {2021-03-17},

journal = {Physical Review B},

volume = {103},

number = {10},

pages = {L100503},

abstract = {To investigate spin susceptibility in a superconducting (SC) state, we measured the 125 Te -NMR Knight shifts at magnetic fields ( H ) up to 6.5 T along the b and c axes of single-crystal UTe 2 , a promising candidate for a spin-triplet superconductor. In the SC state, the Knight shifts along the b and c axes ( K b and K c , respectively) decreased slightly, and the decrease in K b was almost constant up to 6.5 T. The reduction in K c decreased with increasing H , and K c was unchanged through the SC transition temperature at 5.5 T, excluding the possibility of spin-singlet pairing. Our results indicate that spin susceptibilities along the b and c axes slightly decrease in the SC state in low H , and the H response of SC spin susceptibility is anisotropic on the b c plane. We discuss the possible d -vector state within the spin-triplet scenario and suggest that the dominant d -vector component for the case of H ∥ b changes above 13 T, where T c increases with increasing H .},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{SRO_heatcapacity_uniax,

title = {High-sensitivity heat-capacity measurements on Sr2RuO4 under uniaxial pressure},

author = {Y-S Li and N Kikugawa and D A Sokolov and F Jerzembeck and A S Gibbs and Y Maeno and C W Hicks and J Schmalian and M Nicklas and A P Mackenzie},

editor = {Z Fisk },

doi = {10.1073/pnas.2020492118},

year  = {2021},

date = {2021-03-09},

journal = {PNAS},

volume = {118},

number = {10},

abstract = {A key question regarding the unconventional superconductivity of Sr2RuO4 remains whether the order parameter is single- or two-component. Under a hypothesis of two-component superconductivity, uniaxial pressure is expected to lift their degeneracy, resulting in a split transition. The most direct and fundamental probe of a split transition is heat capacity. Here, we report measurement of heat capacity of samples subject to large and highly homogeneous uniaxial pressure. We place an upper limit on the heat-capacity signature of any second transition of a few percent of that of the primary superconducting transition. The normalized jump in heat capacity, ΔC/C, grows smoothly as a function of uniaxial pressure, favoring order parameters which are allowed to maximize in the same part of the Brillouin zone as the well-studied van Hove singularity. Thanks to the high precision of our measurements, these findings place stringent constraints on theories of the superconductivity of Sr2RuO4.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yamamoto_NC_2020,

title = {Strain-induced creation and switching of anion vacancy layers in perovskite oxynitrides},

author = {T Yamamoto and A Chikamatsu and S Kitagawa and N Izumo and S Yamashita and H Takatsu and M Ochi and T Maruyama and M Namba and W Sun and T Nakashima and F Takeiri and K Fujii and M Yashima and Y Sugisawa and M Sano and Y Hirose and D Sekiba and C M Brown and T Honda and K Ikeda and T Otomo and K Kuroki and K Ishida and T Mori and K Kimoto and T Hasegawa and H Kageyama},

doi = {10.1038/s41467-020-19217-7},

year  = {2020},

date = {2020-11-23},

journal = {Nature Communications},

volume = {11},

pages = {5923},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{mattoni2020role,

title = {Role of local temperature in the current-driven metal–insulator transition of Ca_{2}RuO_{4}},

author = {G Mattoni and S Yonezawa and F Nakamura and Y Maeno},

url = {https://arxiv.org/abs/2007.06885},

doi = {10.1103/PhysRevMaterials.4.114414},

year  = {2020},

date = {2020-11-17},

journal = {Physical Review Materials},

volume = {4},

number = {114414},

abstract = {It was recently reported that a continuous electric current is a powerful control parameter to trigger changes in the electronic structure and metal–insulator transitions (MITs) in Ca2RuO4. However, the spatial evolution of the MIT and the implications of the unavoidable Joule heating have not been clarified yet, often hindered by the difficulty to assess the local sample temperature. In this work, we perform infrared thermal imaging on single-crystal Ca2RuO4 while controlling the MIT by electric current. The change in emissivity at the phase transition allows us to monitor the gradual formation and expansion of the metallic phase upon increasing current. Our local temperature measurements indicate that, within our experimental resolution, the MIT always occurs at the same local transition temperatures, irrespective of whether it is driven by temperature or current. Our results highlight the importance of local heating, phase coexistence, and microscale inhomogeneity when studying strongly correlated materials under the flow of electric current.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{SRO_ultrasound,

title = {Ultrasound evidence for a two-component superconducting order parameter in Sr2RuO4},

author = {S. Benhabib and C. Lupien and I. Paul and L. Berges and M. Dion and M. Nardone and A. Zitouni and Z. Q. Mao and Y. Maeno and A. Georges and L. Taillefer and C. Proust},

doi = {10.1038/s41567-020-01090-2},

year  = {2020},

date = {2020-10-21},

journal = {Nature Physics},

volume = {17},

pages = {194-198},

abstract = {The quasi-two-dimensional metal Sr2RuO4 is one of the best characterized unconventional superconductors, yet the nature of its superconducting order parameter is still under debate. This information is crucial to determine the pairing mechanism of Cooper pairs. Here we use ultrasound velocity to probe the superconducting state of Sr2RuO4. This thermodynamic probe is sensitive to the symmetry of the material, and therefore, it can help in identifying the symmetry of the superconducting order parameter. Indeed, we observe a sharp jump in the shear elastic constant c66 as the temperature is increased across the superconducting transition. This directly implies that the superconducting order parameter is of a two-component nature. On the basis of symmetry arguments and given the other known properties of Sr2RuO4, we discuss which states are compatible with this requirement and propose that the two-component order parameter {dxz; dyz} is the most likely candidate.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ivan_NatCommun_2020,

title = {Uniaxial-strain control of nematic superconductivity in SrxBi2Se3},

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

doi = {10.1038/s41467-020-17913-y},

year  = {2020},

date = {2020-08-24},

journal = {Nature Communications},

volume = {11},

pages = {4152},

abstract = {Nematic states are characterized by rotational symmetry breaking without translational ordering. Recently, nematic superconductivity, in which the superconducting gap spontaneously lifts the rotational symmetry of the lattice, has been discovered. In nematic superconductivity, multiple superconducting domains with different nematic orientations can exist, and these domains can be controlled by a conjugate external stimulus. Domain engineering is quite common in magnets but has not been achieved in superconductors. Here, we report control of the nematic superconductivity and their domains of SrxBi2Se3, through externally-applied uniaxial stress. The suppression of subdomains indicates that it is the Δ4y state that is most favoured under compression along the basal Bi-Bi bonds. This fact allows us to determine the coupling parameter between the nematicity and lattice distortion. These results provide an inevitable step towards microscopic understanding and future utilization of the unique topological nematic superconductivity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno_FC_2020,

title = {Three related topics on the periodic tables of elements},

author = {Y Maeno and K Hagino and T Ishiguro },

doi = {10.1007/s10698-020-09387-z},

year  = {2020},

date = {2020-08-18},

journal = {Foundations of Chemistry},

abstract = {A large variety of periodic tables of the chemical elements have been proposed. It was Mendeleev who proposed a periodic table based on the extensive periodic law and predicted a number of unknown elements at that time. The periodic table currently used worldwide is of a long form pioneered by Werner in 1905. As the first topic, we describe the work of Pfeiffer (Naturwiss. 8:984–991, 1920), who refined Werner’s work and rearranged the rare-earth elements in a separate table below the main table for convenience. Today’s widely used periodic table essentially inherits Pfeiffer’s arrangements. Although long-form tables more precisely represent electron orbitals around a nucleus, they lose some of the features of Mendeleev’s short-form table to express similarities of chemical properties of elements when forming compounds. As the second topic, we compare various three-dimensional (3D) helical periodic tables that resolve some of the shortcomings of the long-form periodic tables in this respect. In particular, we explain how the 3D periodic table “Elementouch” (Maeno in Periodic-table-of-the-elements stationery. Design No. 1149493, Japan Patent Office. https://www.j-platpat.inpit.go.jp/d0000, 2001), which combines the s- and p-blocks into one tube, can recover features of Mendeleev’s periodic law. Finally we introduce a topic on the recently proposed nuclear periodic table based on the proton magic numbers (Hagino and Maeno in Found Chem 22:267–273, 2020). Here, the nuclear shell structure leads to a new arrangement of the elements with the proton magic-number nuclei treated like noble-gas atoms. We show that the resulting alignments of the elements in both the atomic and nuclear periodic tables are common over about two thirds of the tables because of a fortuitous coincidence in their magic numbers.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Okuno_JPSJ_2020,

title = {Magnetic-Field Dependence of Novel Gap Behavior Related to the Quantum-Size Effect},

author = {T Okuno and Y Kinoshita and S Matsuzaki and S Kitagawa and K Ishida and M Hirata and T Sasaki and K Kusada and H Kitagawa},

url = {https://arxiv.org/abs/2007.07688},

doi = {10.7566/JPSJ.89.095002},

year  = {2020},

date = {2020-08-03},

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

volume = {89},

number = {9},

pages = {095002},

abstract = {195Pt-NMR measurements of Pt nanoparticles with a mean diameter of 4.0 nm were performed in a high magnetic field of approximately μ0H = 23.3 T to investigate the low-temperature electronic state of the nanoparticles. The characteristic temperature T*, below which the nuclear spin-lattice relaxation rate 1/T1 deviates from the relaxation rate of the bulk, shows a magnetic-field dependence. This dependence supports the theoretical prediction of the appearance of discrete energy levels.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ikeda_PRB_2020,

title = {Penetration depth and gap structure in the antiperovskite oxide superconductor Sr_{3−x}SnO revealed by μSR},

author = {A Ikeda and Z Guguchia and M Oudah and S Koibuchi and S Yonezawa and D Das and T Shiroka and H Luetkens and Y Maeno},

url = {http://hdl.handle.net/2433/250921

https://arxiv.org/abs/2004.06993},

doi = {10.1103/PhysRevB.101.174503},

year  = {2020},

date = {2020-05-04},

journal = {Physical Review B},

volume = {101},

number = {17},

pages = {174503},

abstract = {We report a μSR study on the antiperovskite oxide superconductor Sr3−xSnO. By using transverse-field μSR, we observed an increase of the muon relaxation rate upon cooling below the superconducting transition temperature Tc =5.4 K, evidencing bulk superconductivity. 

The exponential temperature dependence of the relaxation rate σ at low temperatures suggests a fully gapped superconducting state. We evaluated the zero-temperature penetration depth λ(0) ∝ 1/√σ(0) to be around 320–1020 nm. Such a large value is consistent with the picture of a doped Dirac semimetal. 

Moreover, we established that the ratio Tc/λ(0)−2 is larger than those of ordinary superconductors and is comparable to those of unconventional superconductors. The relatively high Tc for small carrier density may hint at an unconventional pairing mechanism beyond the ordinary phonon-mediated pairing. In addition, zero-field μSR did not provide evidence of broken time-reversal symmetry in the superconducting state. These features are consistent with the theoretically proposed topological superconducting state in Sr3−xSnO, as well as with ordinary s-wave superconductivity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{mattoni2020diamagnetic,

title = {Diamagnetic-like response from localized heating of a paramagnetic material},

author = {G Mattoni and S Yonezawa and Y Maeno},

url = {https://arxiv.org/abs/2004.04570},

doi = {10.1063/5.0006098},

year  = {2020},

date = {2020-04-30},

journal = {Applied Physics Letters},

volume = {116},

number = {17},

pages = {172405},

publisher = {AIP Publishing LLC},

abstract = {In the search of material properties out-of-equilibrium, the non-equilibrium steady states induced by electric current are an appealing research direction where unconventional states may emerge. However, the unavoidable Joule heating caused by flowing current calls for the development of new measurement protocols, with a particular attention to the physical properties of the background materials involved. Here, we demonstrate that localised heating can give rise to a large, spurious diamagnetic-like signal. This occurs due to the local reduction of the background magnetisation caused by the heated sample, provided that the background material has a Curie-like susceptibility. Our experimental results, along with numerical calculations, constitute an important building block for performing accurate magnetic measurements under the flow of electric current.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ikeda_PRR_2020,

title = {Superconductivity in the nonsymmorphic line-nodal compound  CaSb_{2}},

author = {A Ikeda and M Kawaguchi and S Koibuchi and T Hashimoto and T Kawakami and S Yonezawa and M Sato and Y Maeno},

url = {https://arxiv.org/abs/2003.12800},

doi = {10.1103/PhysRevMaterials.4.041801},

year  = {2020},

date = {2020-04-13},

journal = {Physical Review Materials},

volume = {4},

number = {4},

pages = {041801(R)},

abstract = {We found superconductivity in CaSb2 with the transition temperature of 1.7 K by means of electrical-resistivity, magnetic-susceptibility, and specific-heat measurements. This material crystallizes in a nonsymmorphic structure and is predicted to have multiple Dirac nodal lines in the bulk electronic band structure protected by symmetry even in the presence of spin-orbit coupling. We discuss a possible topological superconductivity for the quasi-two-dimensional band originating mainly from one of the antimony sites.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yasui2020,

title = {Spontaneous emergence of Josephson junctions in homogeneous rings of single-crystal Sr_{2}RuO_{4}},

author = {Y Yasui and K Lahabi and V F Becerra and R Fermin and M S Anwar and S Yonezawa and T Terashima and M V Milošević and J Aarts and Y Maeno},

url = {https://arxiv.org/abs/2002.06728},

doi = {10.1038/s41535-020-0223-7},

year  = {2020},

date = {2020-04-09},

journal = {npj Quantum Materials},

volume = {5},

number = {1},

abstract = {The chiral p-wave order parameter in Sr2RuO4 would make it a special case amongst the unconventional superconductors. A consequence of this symmetry is the possible existence of superconducting domains of opposite chirality. At the boundary of such domains, the locally suppressed condensate can produce an intrinsic Josephson junction. Here, we provide evidence of such junctions using mesoscopic rings, structured from Sr2RuO4 single crystals. Our order parameter simulations predict such rings to host stable domain walls across their arms. This is verified with transport experiments on loops, with a sharp transition at 1.5 K, which show distinct critical current oscillations with periodicity corresponding to the flux quantum. In contrast, loops with broadened transitions at around 3 K are void of such junctions and show standard Little–Parks oscillations. Our analysis demonstrates the junctions are of intrinsic origin and makes a compelling case for the existence of superconducting domains. © 2020, The Author(s).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{S_Kitagawa2020,

title = {Variation in Superconducting Symmetry Against Pressure on Noncentrosymmetric Superconductor Cd_{2}Re_{2}O_{7} Revealed by ^{185/187}Re Nuclear Quadrupole Resonance},

author = {S Kitagawa and K Ishida and T C Kobayashi and Y Matsubayashi and D Hirai and Z Hiroi},

url = {https://arxiv.org/abs/2004.00919},

doi = {10.7566/JPSJ.89.053701},

year  = {2020},

date = {2020-04-02},

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

volume = {89},

number = {5},

pages = {053701},

abstract = {We performed 185/187Re nuclear quadrupole resonance (NQR) measurements under pressure to investigate the superconducting properties of noncentrosymmetric superconductor Cd2Re2O7 under various crystal structures. The pressure dependence of superconducting transition temperature Tc determined through ac susceptibility measurements is consistent with the results of previous resistivity measurements [Kobayashi et al., J. Phys. Soc. Jpn. 80, 023715 (2011)]. Below 2.2 GPa, in the nuclear spin–lattice relaxation rate 1/T1, a clear coherence peak was observed just below Tc, indicating conventional s-wave superconductivity. In contrast, the coherence peak disappears at 3.1 GPa, suggesting a change in superconducting symmetry to the p-wave dominant state against pressure.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Okuno2020,

title = {NMR-based gap behavior related to the quantum size effect},

author = {T Okuno and M Manago and S Kitagawa and K Ishida and K Kusada and H Kitagawa},

url = {https://arxiv.org/abs/2003.07585},

doi = {10.1103/PhysRevB.101.121406},

year  = {2020},

date = {2020-03-30},

journal = {Physical Review B},

volume = {101},

number = {12},

abstract = {We conducted Pt195-NMR measurements on various-diameter Pt nanoparticles coated with polyvinylpyrrolidone in order to detect the quantum size effect and the discrete energy levels in the electron density of states, both of which were predicted by Kubo more than 50 years ago. We succeeded in separating the signals arising from the surface and interior regions and found that the nuclear spin-lattice relaxation rates in both regions show the metallic behavior at high temperatures. Surprisingly, the magnetic fluctuations in both regions exhibited anomalous behavior below the same temperature T∗, which points to a clear size dependence and is well scaled with δKubo. These results suggest that a size-tunable metal-insulator transition occurs in the Pt nanoparticles as a result of the quantum size effect. © 2020 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ikeda2019,

title = {Negative ionic states of tin in the oxide superconductor Sr_{3-x}SnO revealed by Mössbauer spectroscopy},

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

url = {http://hdl.handle.net/2433/250418

https://arxiv.org/abs/1911.12934},

doi = {10.1103/PhysRevB.100.245145},

year  = {2019},

date = {2019-12-24},

journal = {Physical Review B},

volume = {10},

number = {24},

pages = {245145},

abstract = {We report the temperature variation of the Sn119-Mössbauer spectra of the antiperovskite (inverse perovskite) oxide superconductor Sr3-xSnO. Both superconductive (Sr deficient) and nonsuperconductive (nearly stoichiometric) samples exhibit major γ-ray absorption with an isomer shift similar to that of Mg2Sn. This fact shows that Sr3-xSnO contains the metallic anion Sn4-, which is rare, especially among oxides. In both samples, we observed another γ-ray absorption with a larger isomer shift, indicating that there is another ionic state of Sn with a higher oxidation number. The temperature dependence of the absorption intensities reveals that the Sn ions exhibiting larger isomer shifts have a lower energy of the local vibration. The larger isomer shift and lower vibration energy are consistent with the values estimated from the first-principles calculations for hypothetical structures with various Sr-deficiency arrangements. Therefore, we conclude that the additional γ-ray absorptions originate from the Sn atoms neighboring the Sr deficiency. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Anwar2019,

title = {Anomalous anisotropic behaviour of spin-triplet proximity effect in Au/SrRuO_{3}/Sr_{2}RuO_{4} junctions},

author = {M S Anwar and M Kunieda and R Ishiguro and S R Lee and C Sow and J W A Robinson and S Yonezawa and T W Noh and Y Maeno},

doi = {10.1038/s41598-019-52003-0},

year  = {2019},

date = {2019-11-01},

journal = {Scientific Reports},

volume = {9},

number = {1},

abstract = {Spin-polarized supercurrents can be generated with magnetic inhomogeneity at a ferromagnet/spin-singlet-superconductor interface. In such systems, complex magnetic inhomogeneity makes it difficult to functionalise the spin-polarized supercurrents. However, spin-polarized supercurrents in ferromagnet/spin-triplet-superconductor junctions can be controlled by the angle between magnetization and spin of Copper pairs (d-vector), that can effectively be utilized in developing of a field of research known as superconducting spintronics. Recently, we found induction of spin-triplet correlation into a ferromagnet SrRuO3 epitaxially deposited on a spin-triplet superconductor Sr2RuO4, without any electronic spin-flip scattering. Here, we present systematic magnetic field dependence of the proximity effect in Au/SrRuO3/Sr2RuO4 junctions. It is found that induced triplet correlations exhibit strongly anisotropic field response. Such behaviour is attributed to the rotation of the d-vector of Sr2RuO4. This anisotropic behaviour is in contrast with the vortex dynamic. Our results will stimulate study of interaction between ferromagnetism and unconventional superconductivity. © 2019, The Author(s).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Manago2019c,

title = {Superconductivity at the pressure-induced ferromagnetic critical region in UCoGe},

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

doi = {10.7566/JPSJ.88.113704},

year  = {2019},

date = {2019-10-23},

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

volume = {88},

number = {11},

abstract = {The phase separation of the ferromagnetic (FM) and paramagnetic (PM) phases in the superconducting (SC) state of UCoGe at the FM critical region was investigated using 59Co nuclear quadrupole resonance (NQR) technique by taking advantage of its site-selective feature. The NQR measurements revealed that the first-order quantum phase transition occurs between the FM and the PM states. The nuclear spin–lattice relaxation rate 1=T1 exhibited a clear drop at the SC state in the PM phase, whereas it was not detected in the FM phase, which indicates that the superconductivity in the FM phase becomes weaker at the FM critical region due to the presence of the PM SC state. This result suggests that the SC condensation energy of the PM SC state is equal or larger than that of the FM SC state in this region. The pressure–temperature phase diagram of UCoGe was modified by taking the results from this study into account. ©2019 The Physical Society of Japan},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nakamine2019b,

title = {Superconducting Properties of Heavy Fermion UTe_{2} Revealed by ^{125}Te-nuclear Magnetic Resonance},

author = {G Nakamine and S Kitagawa and K Ishida and Y Tokunaga and H Sakai and S Kambe and A Nakamura and Y Shimizu and Y Homma and D Li and F Honda and D Aoki},

doi = {10.7566/JPSJ.88.113703},

year  = {2019},

date = {2019-10-17},

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

volume = {88},

number = {11},

abstract = {We have performed the 125Te-nuclear magnetic resonance (NMR) measurement in the field along the b axis on the newly discovered superconductor UTe2, which is a candidate of a spin-triplet superconductor. The nuclear spin–lattice relaxation rate divided by temperature 1=T1T abruptly decreases below a superconducting (SC) transition temperature Tc without showing a coherence peak, indicative of UTe2 being an unconventional superconductor. It was found that the temperature dependence of 1=T1T in the SC state cannot be understood by a single SC gap behavior but can be explained by a two SC gap model. The Knight shift, proportional to the spin susceptibility, decreases below Tc, but the magnitude of the decrease is much smaller than the decrease expected in the spin-singlet pairing. Rather, the small Knight-shift decrease as well as the absence of the Pauli-depairing effect can be interpreted by the spin triplet scenario. © 2019 Society The Author(s) of Japan.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kashiwaya2019,

title = {Time-reversal invariant superconductivity of Sr_{2}RuO_{4} revealed by Josephson effects},

author = {S Kashiwaya and K Saitoh and H Kashiwaya and M Koyanagi and M Sato and K Yada and Y Tanaka and Y Maeno},

doi = {10.1103/PhysRevB.100.094530},

year  = {2019},

date = {2019-09-25},

journal = {Physical Review B},

volume = {100},

number = {9},

abstract = {Sr2RuO4 is one of the most promising candidates of a topological superconductor with broken time-reversal symmetry because a number of experiments have revealed evidence for a spin-triplet chiral p-wave superconductivity. To clarify the time-reversal symmetry of Sr2RuO4, we introduce a test that examines the invariance of the Josephson critical current under the inversion of both the current and magnetic fields, in contrast to the detection of a spontaneous magnetic field employed in past experiments. Analyses of the transport properties of the planar and corner Josephson junctions formed between Sr2RuO4 and Nb reveal the time-reversal invariant superconductivity, most probably helical p-wave symmetry, of Sr2RuO4. This state corresponds to a yet-to-be confirmed topological crystalline superconductivity that can host two Majorana edge modes at the surface protected by crystalline mirror symmetry. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitagawa2019,

title = {Universal relationship between low-energy antiferromagnetic fluctuations and superconductivity in BaFe_{2}(As_{1-x}P_{x})_{2}},

author = {S Kitagawa and T Kawamura and K Ishida and Y Mizukami and S Kasahara and T Shibauchi and T Terashima and Y Matsuda},

doi = {10.1103/PhysRevB.100.060503},

year  = {2019},

date = {2019-08-12},

journal = {Physical Review B},

volume = {100},

number = {6},

abstract = {To identify the key parameter for optimal superconductivity in iron pnictides, we measured the P31-NMR relaxation rate on BaFe2(As1-xPx)2(x=0.22 and 0.28) under pressure and compared the effects of chemical substitution and physical pressure. For x=0.22, structural and antiferromagnetic (AFM) transition temperatures both show minimal changes with pressure up to 2.4 GPa, whereas the superconducting transition temperature Tc increases to twice its former value. In contrast, for x=0.28 near the AFM quantum critical point (QCP), the structural phase transition is quickly suppressed by pressure and Tc reaches a maximum. The analysis of the temperature-dependent nuclear relaxation rate indicates that these contrasting behaviors can be quantitatively explained by a single curve of the Tc dome as a function of Weiss temperature θ, which measures the distance to the QCP. Moreover, the Tc-θ curve under pressure precisely coincides with that with a chemical substitution, which is indicative of the existence of a universal relationship between low-energy AFM fluctuations and superconductivity on BaFe2(As1-xPx)2. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Anwar2019b,

title = {Observation of superconducting gap spectra of long-range proximity effect in Au/SrTiO_{3}/SrRuO_{3}/Sr_{2}RuO_{4} tunnel junctions},

author = {M S Anwar and M Kunieda and R Ishiguro and S R Lee and L A B O Olthof and J W A Robinson and S Yonezawa and T W Noh and Y Maeno},

doi = {10.1103/PhysRevB.100.024516},

year  = {2019},

date = {2019-07-24},

journal = {Physical Review B},

volume = {100},

number = {2},

abstract = {We observe an unconventional superconducting minigap induced into a ferromagnet SrRuO3 from a spin-triplet superconductor Sr2RuO4 using an Au/SrTiO3/SrRuO3/Sr2RuO4 tunnel junction. Voltage bias differential conductance of the tunnel junctions exhibits V-shaped gap features around zero bias, corresponding to a decrease in the density of states with an opening of a superconducting minigap in SrRuO3. Observation of a minigap at the surface of a 15-nm-thick SrRuO3 layer confirms the spin-triplet nature of induced superconductivity. The shape and temperature dependence of the gap features in the differential conductance suggest that the even-frequency p-wave correlations dominate over odd-frequency s-wave correlations. Theoretical calculations support this p-wave scenario. Our work provides the density-of-states proof for an induced minigap in a ferromagnet, and it significantly advanced our understanding of the spin-triplet proximity effect between unconventional superconductors and ferromagnets. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Asano2019,

title = {Oxidation annealing effects on the spin-glass-like magnetism and appearance of superconductivity in T*-type La_{1−x/2}Eu_{1−x/2}Sr_{x}CuO_{4} (0.14 ≤ x ≤ 0.28)},

author = {S Asano and K M Suzuki and K Kudo and I Watanabe and A Koda and R Kadono and T Noji and Y Koike and T Taniguchi and S Kitagawa and K Ishida and M Fujita},

doi = {10.7566/JPSJ.88.084709},

year  = {2019},

date = {2019-07-23},

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

volume = {88},

number = {8},

abstract = {We investigated the magnetism and superconductivity in as-sintered (AS) and oxidation annealed (OA) T+-type La1−x=2Eu1−x=2SrxCuO4 (LESCO) with 0.14 ≤ x ≤ 0.28 by the first comprehensive muon spin rotation=relaxation (μSR), magnetic susceptibility, and electrical resistivity measurements. In OA superconducting samples, no evidence of magnetic order was observed, whereas AS semiconducting samples exhibited evidence of a disordered magnetic state in the measured temperature range between ∼4 and ∼8 K. Therefore, the ground state in LESCO drastically varies with oxidation annealing and the magnetic phase competitively exists with the superconducting (SC) phase. The magnetic phase in the AS LESCO is quite robust against Sr doping, while the SC phase degrades with increasing x. A monotonous decrease of the SC transition temperature from 24.5 K in x = 0.14 to 9.0 K in x = 0.28 suggests the disappearance of the SC phase at x ∼ 0.34. Furthermore, we clarified the simultaneous development of (quasi) static magnetism and the electrical resistivity at a low temperature in AS samples, suggesting the inducement of magnetism by the suppression of carrier mobility. The variation in magnetism due to annealing is discussed from a viewpoint of structural defects, which was previously reported from neutron diffraction measurements. ©2019 The Physical Society of Japan},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Manago2019,

title = {Spin-triplet superconductivity in the paramagnetic UCoGe under pressure studied by ^{59}Co NMR},

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

doi = {10.1103/PhysRevB.100.035203},

year  = {2019},

date = {2019-07-12},

journal = {Physical Review B},

volume = {100},

number = {3},

abstract = {A Co59 nuclear magnetic resonance (NMR) measurement was performed on the single-crystalline ferromagnetic (FM) superconductor UCoGe under a pressure of 1.09 GPa, where the FM state is suppressed and superconductivity occurs in the paramagnetic (PM) state, to study the superconducting (SC) state in the PM state. Co59-NMR spectra became broader but hardly shifted across the SC transition temperature. The Knight-shift change determined from fitting the spectral peak with a Gaussian was much smaller than the spin part of the Knight shift; this is in good agreement with the spin-triplet pairing suggested from the large upper critical field. The spectrum broadening in the SC state cannot be attributed to the SC diamagnetic effect but is related to the properties of spin-triplet superconductivity. The origins of the broadening are discussed herein. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tokunaga2019,

title = {^{125}Te-NMR study on a single crystal of heavy fermion superconductor UTe_{2}},

author = {Y Tokunaga and H Sakai and S Kambe and T Hattori and N Higa and G Nakamine and S Kitagawa and K Ishida and A Nakamura and Y Shimizu and Y Homma and D Li and F Honda and D Aoki},

doi = {10.7566/JPSJ.88.073701},

year  = {2019},

date = {2019-06-24},

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

volume = {88},

number = {7},

abstract = {We report 125Te NMR studies on a newly discovered heavy fermion superconductor UTe2. Using a single crystal, we have measured the 125Te NMR Knight shift K and spin-lattice relaxation rate 1=T1 for fields along the three orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for both the static (K) and dynamical susceptibilities (1=T1) in the paramagnetic state above about 20 K. Around 20 K, however, we have observed a sudden loss of NMR spin-echo signal due to sudden enhancement of the NMR spin-spin relaxation rate 1=T2, when the field is applied along the easy axis of magnetization (= a-axis). This behavior suggests the development of longitudinal magnetic fluctuations along the a-axis at very low frequencies below 20 K. © 2019 The Physical Society of Japan},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kinjo2019,

title = {Magnetic field effect on s-wave superconductor LaRu_{4}P_{12} Studied by ^{31}P-NMR},

author = {K Kinjo and S Kitagawa and Y Nakai and K Ishida and H Sugawara and H Sato},

doi = {10.7566/JPSJ.88.065002},

year  = {2019},

date = {2019-05-30},

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

volume = {88},

number = {6},

abstract = {We have performed 31P-NMR measurements on the s-wave superconductor LaRu4P12 to investigate the magnetic field effect of the nuclear spin–lattice relaxation rate 1=T1 on a conventional full-gap superconductor. With increasing magnetic field, the Hebel–Slichter peak immediately below Tc in 1=T1 was suppressed, and the magnetic field dependence of 1=T1 at 0.8K, well below Tc, was proportional to H2. These behaviors can be fully understood by the orbital pair-breaking effect in a single-band s-wave superconductor. © 2019 The Physical Society of Japan},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Sow2019,

title = {In situ control of diamagnetism by electric current in Ca_{3}(Ru_{1-x}Ti_{x})_{2}O_{7}},

author = {C Sow and R Numasaki and G Mattoni and S Yonezawa and N Kikugawa and S Uji and Y Maeno},

url = {https://arxiv.org/abs/1902.02515},

doi = {10.1103/PhysRevLett.122.196602},

year  = {2019},

date = {2019-05-17},

journal = {Physical Review Letters},

volume = {122},

number = {19},

abstract = {Nonequilibrium steady state conditions induced by a dc current can alter the physical properties of strongly correlated electron systems. In this regard, it was recently shown that dc current can trigger novel electronic states, such as current-induced diamagnetism, which cannot be realized in equilibrium conditions. However, reversible control of diamagnetism has not been achieved yet. Here, we demonstrate reversible in situ control between a Mott insulating state and a diamagnetic semimetal-like state by a dc current in the Ti-substituted bilayer ruthenate Ca3(Ru1-xTix)2O7 (x=0.5%). By performing simultaneous magnetic and resistive measurements, we map out the temperature vs current-density phase diagram in the nonequilibrium steady state of this material. The present results open up the possibility of creating novel electronic states in a variety of strongly correlated electron systems under dc current. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lee2019,

title = {Strong spin-phonon coupling unveiled by coherent phonon oscillations in Ca_{2}RuO_{4}},

author = {M -C Lee and C H Kim and I Kwak and C W Seo and C Sohn and F Nakamura and C Sow and Y Maeno and E -A Kim and T W Noh and K W Kim},

doi = {10.1103/PhysRevB.99.144306},

year  = {2019},

date = {2019-04-15},

journal = {Physical Review B},

volume = {99},

number = {14},

abstract = {We utilize near-infrared femtosecond pulses to investigate coherent phonon oscillations of Ca2RuO4. The coherent Ag phonon mode of the lowest frequency changes abruptly not only its amplitude but also the oscillation phase as the spin order develops. In addition, the phonon mode shows a redshift entering the magnetically ordered state, which indicates a spin-phonon coupling in the system. Density functional theory calculations reveal that the Ag oscillations result in octahedral tilting distortions, which are exactly in sync with the lattice deformation driven by the magnetic ordering. We suggest that the structural distortions by the spin-phonon coupling can induce the unusual oscillation phase shift between impulsive and displacive type oscillations. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nakamine2019,

title = {Modification of magnetic fluctuations by interfacial interactions in artificially engineered heavy-fermion superlattices},

author = {G Nakamine and T Yamanaka and S Kitagawa and M Naritsuka and T Ishii and T Shibauchi and T Terashima and Y Kasahara and Y Matsuda and K Ishida},

doi = {10.1103/PhysRevB.99.081115},

year  = {2019},

date = {2019-02-19},

journal = {Physical Review B},

volume = {99},

number = {8},

abstract = {Recent progress in the fabrication techniques of superlattices (SLs) has made it possible to sandwich several-layer-thick block layers (BLs) of heavy-fermion superconductor CeCoIn5 between conventional-metal YbCoIn5 BLs or spin-density-wave-metal CeRhIn5 BLs of a similar thickness. However, the magnetic state in each BL, particularly at the interface, is not yet understood, as experimental techniques applicable to the SL system are limited. Here, we report measurements of Co59 nuclear magnetic resonance, which is a microscopic probe of the magnetic properties inside the target BLs. In the CeCoIn5/YbCoIn5 SL, the low-temperature magnetic fluctuations of the CeCoIn5 BL are weakened as expected from the Rashba spin-orbit effect. However, in the CeCoIn5/CeRhIn5 SL, the fluctuations show an anomalous enhancement below 6 K, highlighting the importance of the magnetic proximity effect occurring near a magnetic-ordering temperature TN∼3 K of the CeRhIn5 BL. We suggest that the magnetic properties of the BLs can be altered by the interfacial interaction, which is an alternative route to modify the magnetic properties. © 2019 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zhang2019,

title = {Nano-Resolved Current-Induced Insulator-Metal Transition in the Mott Insulator Ca_{2}RuO_{4}},

author = {J Zhang and A S McLeod and Q Han and X Chen and H A Bechtel and Z Yao and S N Gilbert Corder and T Ciavatti and T H Tao and M Aronson and G L Carr and M C Martin and C Sow and S Yonezawa and F Nakamura and I Terasaki and D N Basov and A J Millis and Y Maeno and M Liu},

doi = {10.1103/PhysRevX.9.011032},

year  = {2019},

date = {2019-02-15},

journal = {Physical Review X},

volume = {9},

number = {1},

abstract = {The Mott insulator Ca2RuO4 is the subject of much recent attention following reports of emergent nonequilibrium steady states driven by applied electric fields or currents. In this paper, we carry out infrared nano-imaging and optical-microscopy measurements on bulk single crystal Ca2RuO4 under conditions of steady current flow to obtain insight into the current-driven insulator-to-metal transition. We observe macroscopic growth of the current-induced metallic phase, with nucleation regions for metal and insulator phases determined by the polarity of the current flow. A remarkable metal-insulator-metal microstripe pattern is observed at the phase front separating metal and insulator phases. The microstripes have orientations tied uniquely to the crystallographic axes, implying a strong coupling of the electronic transition to lattice degrees of freedom. Theoretical modeling further illustrates the importance of the current density and confirms a submicron-thick surface metallic layer at the phase front of the bulk metallic phase. Our work confirms that the electrically induced metallic phase is nonfilamentary and is not driven by Joule heating, revealing remarkable new characteristics of electrically induced insulator-metal transitions occurring in functional correlated oxides. © 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International 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}

}