堀 文哉

@article{F.Hori_JPSJ_2024,

title = {Magnetic-Field Dependence of Paramagnetic Properties Investigated by 63/65Cu-NMR on the Yb Zigzag-Chain Semiconductor YbCuS2},

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

url = {https://arxiv.org/abs/2502.00830},

doi = {10.7566/JPSJ.94.024706},

year  = {2025},

date = {2025-01-29},

urldate = {2025-01-29},

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

volume = {94},

pages = {024706},

abstract = {To investigate the paramagnetic properties of YbCuS2 under magnetic fields, we have performed the 63/65Cu-nuclear magnetic resonance (NMR) measurements. The NMR spectra can be reproduced by the simulations of the three-dimensional powder pattern and the additional two-dimensional powder pattern, indicating the partial sample orientation due to the anisotropy of the magnetic properties. These simulations suggest that the ac plane is the easy plane in YbCuS2. The Knight shift K is proportional to the bulk magnetic susceptibility and field-independent. The broad maximum of the nuclear spin–lattice relaxation rate 1/T1 at Tmax ∼ 50 K (50 K anomaly) observed at zero magnetic field is quickly suppressed by the magnetic fields. This indicates that the 50 K anomaly is field-dependent. Furthermore, an anomalous enhancement of 1/T1 at low temperatures was observed above 3 T. This field seemingly corresponds to the magnetic field at which a field-induced phase transition occurs below the antiferromagnetic transition temperature TN ∼ 1 K. The changes in 1/T1 observed},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{F.Hori_JPSJ_2024,

title = {Gapped Spin Excitation in Magnetic Ordered State on Yb-Based Zigzag Chain Compound YbAgSe2},

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

url = {https://doi.org/10.7566/JPSJ.93.114702},

doi = {10.7566/JPSJ.93.114702},

year  = {2024},

date = {2024-10-11},

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

volume = {93},

issue = {11},

pages = {114702},

abstract = {We report the 77Se-nuclear magnetic resonance (NMR) results of trivalent Yb zigzag chain compound YbAgSe2, which is a sister compound of YbCuS2. The 77Se-NMR spectrum was reproduced by considering two different Se sites with negative Knight shifts and three-axis anisotropy. Above the Néel temperature TN, the Knight shift is proportional to the bulk magnetic susceptibility. Below TN, the extremely broad signal with weak intensity and the relatively sharp signal coexist, suggesting that one is strongly influenced by internal magnetic fields and the other remains relatively unaffected by these fields in the magnetic ordered state. The nuclear spin–lattice relaxation rate 1/T1 remains almost constant above TN and abruptly decreases below TN. In contrast to YbCuS2, a T-linear behavior of 1/T1 at low temperatures was not observed at least down to 1.0 K in YbAgSe2. Our results indicate that the gapless excitation is unique to YbCuS2, or is immediately suppressed in the magnetic fields.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@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{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{nokey,

title = {Impurity-Robust Bulk Gapless Excitation in the Yb-Based Zigzag Chain Compound YbCuS2},

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

doi = {10.1088/1742-6596/2164/1/012027},

year  = {2022},

date = {2022-03-17},

journal = {J. Phys.: Conf. Ser.},

volume = {2164},

pages = {012027},

abstract = {We have performed 63Cu-nuclear quadrupole resonance (NQR) measurements using a lump sample of the Yb zigzag-chain compound YbCuS2 with a small surface area to investigate the sample dependence of low-temperature magnetic properties in YbCuS2 by comparing with the previous study with different powdered sample. The line width of NQR signals in the present lump sample is larger than that in the previous powdered sample. In addition, the transition temperature TN ∼ 0.92 K in the present lump sample is lower than that in the previous powdered sample (∼ 0.95 K). These results suggest that the quality of the present lump sample is worse than that of the previous powdered sample. However, the T-linear behavior of the nuclear spin-lattice relaxation rate 1/T1 was observed below 0.5 K and the value of 1/T1T in both samples is almost the same even though the sample quality and sample geometry are different. This suggests that T-linear behavior in 1/T1 arises from the impurity-robust bulk gapless excitation inherent in YbCuS2 rather than from sample issues such as the sample quality or geometry.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}