北川 俊作

@article{nokey,

title = {Superconducting spin reorientation in spin-triplet multiple superconducting phases of UTe2},

author = {K Kinjo and H Fujibayashi and H Matsumura and F Hori 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/2307.15784},

doi = {10.1126/sciadv.adg2736},

year  = {2023},

date = {2023-07-28},

urldate = {2023-07-28},

journal = {Science Advances},

volume = {9},

pages = {adg2736},

abstract = {Superconducting (SC) state has spin and orbital degrees of freedom, and spin-triplet superconductivity shows multiple SC phases because of the presence of these degrees of freedom. However, the observation of spin-direction rotation occurring inside the SC state (SC spin rotation) has hardly been reported. Uranium ditelluride, a recently found topological superconductor, exhibits various SC phases under pressure: SC state at ambient pressure (SC1), high-temperature SC state above 0.5 gigapascal (SC2), and low-temperature SC state above 0.5 gigapascal (SC3). We performed nuclear magnetic resonance (NMR) and ac susceptibility measurements on a single-crystal uranium ditelluride. The b axis spin susceptibility remains unchanged in SC2, unlike in SC1, and decreases below the SC2-SC3 transition with spin modulation. These unique properties in SC3 arise from the coexistence of two SC order parameters. Our NMR results confirm spin-triplet superconductivity with SC spin parallel to b axis in SC2 and unveil the remaining of spin degrees of freedom in SC uranium ditelluride.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Gapless fermionic excitation in the antiferromagnetic state of ytterbium zigzag chain},

author = {F Hori and K Kinjo and S Kitagawa and K Ishida and S Mizutani and R Yamamoto and Y Ohmagari and T Onimaru },

url = {https://arxiv.org/abs/2201.07563},

doi = {10.1038/s43246-023-00381-4},

year  = {2023},

date = {2023-07-22},

urldate = {2023-07-22},

journal = {Communications Materials},

volume = {4},

pages = {55},

abstract = {The emergence of charge-neutral fermionic excitations in magnetic systems is one of the unresolved issues in recent condensed matter physics. This type of excitations has been observed in various systems, such as low-dimensional quantum spin liquids, Kondo insulators, and antiferromagnetic insulators. Here, we report the presence of a pronounced gapless spin excitation in the low-temperature antiferromagnetic state of YbCuS2 semiconductor, where trivalent ytterbium atoms form a zigzag chain structure. We confirm the presence of this gapless excitations by a combination of experimental probes, namely 63/65Cu-nuclear magnetic resonance and nuclear quadrupole resonance, as well as specific heat measurements, revealing a linear low-temperature behavior of both the nuclear spin-lattice relaxation rate 1/T1 and the specific heat. This system provides a platform to investigate the origin of gapless excitations in spin chains and the relationship between emergent fermionic excitations and frustration.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{H.Matsumura_JPSJ_2023,

title = {Large Reduction in the a-axis Knight Shift on UTe2 with Tc = 2.1 K},

author = {H Matsumura and H Fujibayashi 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/2305.01200},

doi = {10.7566/JPSJ.92.063701},

year  = {2023},

date = {2023-05-16},

urldate = {2023-05-16},

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

volume = {92},

pages = {063701},

abstract = {Spin susceptibility in the superconducting (SC) state was measured in the higher-quality sample of uranium-based superconductor UTe2 by using Knight-shift measurements for a magnetic field H along all three crystalline axes. In the higher-quality sample, the SC transition temperature Tc is about 2.1 K, and the residual electronic term in the specific heat is almost zero. The NMR linewidth becomes narrower and is almost half of that in the previous sample with Tc ∼ 1.6 K when H || a and c. Although the Knight-shift behavior was not so different from the previous results for H || b, and c, a large reduction in Knight shift along the a axis was observed, in contrast with the previous a-axis Knight shift result. We discuss the origin of the difference between the previous and present results, and the possible SC state derived from the present results.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{H.Fujibayashi_JPSJ_2023,

title = {Low-Temperature Magnetic Fluctuations Investigated by 125Te-NMR on the Uranium-Based Superconductor UTe2},

author = {H Fujibayashi and K Kinjo 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},

doi = {10.7566/JPSJ.92.053702},

year  = {2023},

date = {2023-04-26},

urldate = {2023-04-26},

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

volume = {92},

pages = {053702},

abstract = {To investigate the static and dynamic magnetic properties on the uranium-based superconductor UTe2, we measured the NMR Knight shift K and the nuclear spin–lattice relaxation rate 1/T1 in H || a by 125Te-NMR on a 125Te-enriched single-crystal sample. 1/T1T in H || a is much smaller than 1/T1T in H || b and c, and magnetic fluctuations along each axis are derived from the 1/T1T measured in H parallel to all three crystalline axes. The magnetic fluctuations are almost identical at two Te sites and isotropic at high temperatures, but become anisotropic below 40 K, where heavy-fermion state is formed. The character of magnetic fluctuations in UTe2 is discussed with the comparison to its static susceptibility and the results on other U-based superconductors. It is considered that the magnetic fluctuations probed with the NMR measurements are determined by the magnetic properties inside the two-leg ladder formed by U atoms, which are dominated by the qa = 0 ferromagnetic fluctuations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{S.Ogata_PRL_2023,

title = {Parity transition of spin-singlet superconductivity using sub-lattice degrees of freedom},

author = {S Ogata and S Kitagawa and K Kinjo and K Ishida and M Brando and E Hassinger and C Geibel and S Khim},

url = {https://arxiv.org/abs/2304.10032},

doi = {10.1103/PhysRevLett.130.166001},

year  = {2023},

date = {2023-04-19},

urldate = {2023-04-19},

journal = {Physical Review Letters},

volume = {130},

pages = {166001 },

abstract = {Recently, a superconducting (SC) transition from low-field (LF) to high-field (HF) SC states was reported in CeRh2As2, indicating the existence of multiple SC states. It has been theoretically noted that the existence of two Ce sites in the unit cell, the so-called sub-lattice degrees of freedom owing to the local inversion symmetry breaking at the Ce sites, can lead to the appearance of multiple SC phases even under an interaction inducing spin-singlet superconductivity. CeRh2As2 is considered as the first example of multiple SC phases owing to this sub-lattice degree of freedom. However, microscopic information about the SC states has not yet been reported. In this study, we measured the SC spin susceptibility at two crystallographically inequivalent As sites using nuclear magnetic resonance for various magnetic fields. Our experimental results strongly indicate a spin-singlet state in both SC phases. In addition, the antiferromagnetic phase, which appears within the SC phase, only coexists with the LF SC phase; there is no sign of magnetic ordering in the HF SC phase. The present work reveals unique SC properties originating from the locally noncentrosymmetric characteristics. },

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{K.Kinjo_PRB_2023,

title = {Change of superconducting character in UTe2 induced by magnetic field},

author = {K Kinjo and H Fujibayashi 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. X Li and F Honda and D Aoki and K Hiraki and M Kimata and T Sasaki},

url = {https://arxiv.org/abs/2206.02444},

doi = {10.1103/PhysRevB.107.L060502},

year  = {2023},

date = {2023-02-10},

urldate = {2023-02-10},

journal = {Physical Review B},

volume = {107},

issue = {06},

pages = {L060502},

abstract = {UTe2 is a recently discovered spin-triplet superconductor. One of the characteristic features of UTe2 is a magnetic field (H)-boosted superconductivity >16 T when H is applied exactly parallel to the b axis. To date, this superconducting (SC) state has not been thoroughly investigated, and the SC properties as well as the spin state of this high-H SC (HHSC) phase are not well understood. In this letter, we performed AC magnetic susceptibility and nuclear magnetic resonance measurements and found that, up to 24.8 T, the HHSC state has bulk nature and is quite sensitive to the H angle and that its SC character is different from that in the low-H SC (LHSC) state. The dominant spin component of the spin-triplet pair is along the a axis in the LHSC state but is changed in the HHSC state along the b axis. Our results indicate that H -induced multiple SC states originate from the remaining spin degrees of freedom.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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},

url = {https://arxiv.org/abs/2211.15083},

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{T.Taniguchi_JPSJ_2022,

title = {139La-NMR Study of Spin Dynamics Coupled with Hole Mobility in T*-type La0.86Eu0.86Sr0.28CuO4−δ},

author = {T Taniguchi and S Kitagawa and K Ishida and S Asano and K Kudo and M Takahama and P Xie and T Noji and M Fujita},

url = {https://arxiv.org/abs/2110.12333},

doi = {10.7566/JPSJ.91.074710},

year  = {2022},

date = {2022-06-22},

urldate = {2022-06-22},

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

volume = {91},

issue = {07},

pages = {074710},

abstract = {In T*-type cuprate oxides with five-oxygen coordination, the relationship between spin correlations and doped carriers has not been well understood. To clarify this relationship, and the magnetic and superconducting (SC) properties of T*-type cuprate oxides, we performed 139La-nuclear magnetic resonance (NMR) and electrical resistivity measurements on as-sintered (AS) and oxidation-annealed (OA) polycrystalline T*-type La0.86Eu0.86S0.28CuO4 (LESCO) to investigate its magnetic and SC properties. Upon cooling, the NMR spectrum of AS LESCO broadened below 3 K, where the nuclear spin–lattice relaxation rate 1/T1 with respect to the temperature exhibited a maximum, indicating the appearance of static magnetism. The temperature dependence of 1/T1 between 3 and 20 K was similar to that of resistivity, which displays semiconducting behavior. Furthermore, it was found that the energy scales of the transport gap and spin dynamics were comparable. These results suggest a close connection between the mobility of the doped carriers and low-energy spin dynamics, as reported for lightly doped T-type La2−xSrxCuO4. In the OA SC sample, we confirmed the absence of a magnetic order and the linear relation between 1/T1 and T above 10 K. These results suggest that the magnetic state coupled with holes markedly changes to the weakly correlated metallic state by oxidation annealing in the T*-type LESCO with x = 0.28.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}