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Matsumura, Hiroki*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Kimata, Motoi; 14 of others*
Physical Review B, 113(9), p.094506_1 - 094506_12, 2026/03
Times Cited Count：0 Percentile：0.00Sakai, Hideaki*; Kimata, Motoi; 7 of others*
Nature Communications (Internet), 16, p.11112_1 - 11112_8, 2026/01
Times Cited Count：0 Percentile：0.00(Multidisciplinary Sciences)Sudo, Kenta*; Yanagi, Yuki*; Akaki, Mitsuru*; Tanida, Hiroshi*; Kimata, Motoi
Physical Review Letters, 136(1), p.016503_1 - 016503_7, 2026/01
Times Cited Count：0 Percentile：0.00(Physics, Multidisciplinary)Tokiwa, Yoshifumi; Opletal, P.; Sakai, Hironori; Kubo, Katsunori; Kambe, Shinsaku; Yamamoto, Etsuji; Kimata, Motoi; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; et al.
Physical Review Letters, 135(13), p.136502_1 - 136502_6, 2025/09
Times Cited Count：2 Percentile：69.59(Physics, Multidisciplinary)We investigate the effect of easy-axis metamagnetic crossover on superconductivity in UTe along the 
-axis through measurements of AC susceptibility, magnetization, and the magnetocaloric effect. In ultra-clean single crystals, we identify a field-induced phase transition within the superconducting state at 5.6 T, driven by metamagnetism. This transition leads to a high-field superconducting state, significantly increasing the upper critical field to 12 T. A sudden increase in entropy at the transition suggests a self-reconstruction of the order parameter, enabling multi-component superconducting states to adapt to external perturbations.
Karube, Kosuke*; Onuki, Yoshichika*; Nakajima, Taro*; Chen, H.-Y.*; Ishizuka, Hiroaki*; Kimata, Motoi*; Ohara, Takashi; Munakata, Koji*; Nomoto, Takuya*; Arita, Ryotaro*; et al.
npj Quantum Materials (Internet), 10, p.55_1 - 55_9, 2025/06
Times Cited Count：6 Percentile：91.92(Materials Science, Multidisciplinary)
InGeYokoyama, Akira*; Nakachi, Ryu*; Homma, Yoshiya*; Nakamura, Ai*; Shimizu, Yusei*; Li, D.*; Miyake, Atsushi*; Honda, Fuminori*; Aoki, Dai*; Onuki, Yoshichika*; et al.
Journal of the Physical Society of Japan, 94(2), p.023701_1 - 023701_4, 2025/02
Times Cited Count：0 Percentile：0.00(Physics, Multidisciplinary)Tokiwa, Yoshifumi; Opletal, P.; Sakai, Hironori; Kambe, Shinsaku; Yamamoto, Etsuji; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Haga, Yoshinori; et al.
Physical Review B, 109(14), p.L140502_1 - L140502_6, 2024/04
Times Cited Count：8 Percentile：75.29(Materials Science, Multidisciplinary)The normal-conducting state of the superconductor UTe is studied by entropy analysis for magnetic fields along the 
-axis, obtained from magnetization using the relation 
. We observe a strong increase in entropy with magnetic field due to metamagnetic fluctuations (spatially uniform, 
). The field dependence is well described by the Hertz-Millis-Moriya theory for quantum criticality of itinerant metamagnetism. Notably, the lower bound of the quantum-critical region coincides well with the position of the minimum in the superconducting transition temperature 
. Hence, our results suggest that fluctuations reinforce the superconductivity.
Tokiwa, Yoshifumi; Sakai, Hironori; Kambe, Shinsaku; Opletal, P.; Yamamoto, Etsuji; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Yanase, Yoichi*; Haga, Yoshinori; et al.
Physical Review B, 108(14), p.144502_1 - 144502_5, 2023/10
Times Cited Count：10 Percentile：65.50(Materials Science, Multidisciplinary)The vortex dynamics in the spin-triplet superconductor, UTe, are studied by measuring the DC electrical resistivity with currents along the -axis under magnetic fields along the -axis. Surprisingly, we have discovered an island region of low critical current deep inside the superconducting (SC) state, well below the SC upper critical field, attributed to a weakening of vortex pinning. Notably, this region coincides with the recently proposed intermediate-field SC state. We discuss the possibility of nonsingular vortices in the intermediate state, where SC order parameter does not vanish entirely in the vortex cores due to the mixing of multiple SC components.
along hard magnetic axisSakai, Hironori; Tokiwa, Yoshifumi; Opletal, P.; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori
Physical Review Letters, 130(19), p.196002_1 - 196002_6, 2023/05
Times Cited Count：33 Percentile：94.96(Physics, Multidisciplinary)The superconducting (SC) phase diagram in uranium ditelluride is explored under magnetic fields (
) along the hard magnetic -axis using a high-quality single crystal with 
= 2.1 K. Simultaneous electrical resistivity and AC magnetic susceptibility measurements discern low- and high-field SC (LFSC and HFSC, respectively) phases with contrasting field-angular dependence. Crystal quality increases the upper critical field of the LFSC phase, but the 
of 
T, at which the HFSC phase appears, is always the same through the various crystals. A phase boundary signature is also observed inside the LFSC phase near , indicating an intermediate SC phase characterized by small flux pinning forces.
induced by magnetic fieldKinjo, Katsuki*; Fujibayashi, Hiroki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; Homma, Yoshiya*; et al.
Physical Review B, 107(6), p.L060502_1 - L060502_5, 2023/02
Times Cited Count：34 Percentile：92.42(Materials Science, Multidisciplinary)
anisotropic triangular antiferromagnet Ca
ReO
ClNawa, Kazuhiro*; Hirai, Daigoro*; Kofu, Maiko; Nakajima, Kenji; Murasaki, Ryo*; Kogane, Satoshi*; Kimata, Motoi*; Nojiri, Hiroyuki*; Hiroi, Zenji*; Sato, Taku*
Physical Review Research (Internet), 2(4), p.043121_1 - 043121_11, 2020/12
The spin excitations of the 
= anisotropic triangular antiferromagnet CaReOCl were investigated by inelastic neutron-scattering experiments. The spin excitation spectrum exhibits sharp dispersive modes in addition to a spinonlike continuum. The consistency with the simulated spectrum based on the random-phase approximation is better for CaReOCl than for CsCuCl
, indicating that the spin system in the former remains closer to a Tomonaga-Luttinger liquidlike disordered state.
Niimi, Yasuhiro*; Kimata, Motoi*; Omori, Yasutomo*; Gu, B.; Ziman, T.*; Maekawa, Sadamichi; Fert, A.*; Otani, Yoshichika*
Physical Review Letters, 115(19), p.196602_1 - 196602_5, 2015/11
Times Cited Count：14 Percentile：63.15(Physics, Multidisciplinary)Tokiwa, Yoshifumi; Opletal, P.; Sakai, Hironori; Yamamoto, Etsuji; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; et al.
no journal, ,
In unconventional superconductors, there are cases of vortex liquid-like state. When the pinning is strong, vortices do not move, and thus, the formation of such abnormal states requires pure and pristine crystals. Recently, the growth of pure single crystals of the spin-triplet superconductor UTe using a molten salt flux has been reported. In this study, we report research on vortices in UTe using such pure single crystals. As a result, in the magnetic field range of 15 T to 22 T, the critical current showed a maximum in temperature dependence, and a low-temperature region with a low critical current was observed deep in the superconducting state. This low critical current region matches the recently reported intermediate field superconducting phase. This suggests a weakening of the pinning force and a decrease in the critical current in the intermediate field superconducting phase.
Tokiwa, Yoshifumi; Opletal, P.; Sakai, Hironori; Yamamoto, Etsuji; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; et al.
no journal, ,
In unconventional superconductors, there are cases of vortex liquid-like state. When the pinning is strong, vortices do not move, and thus, the formation of such abnormal states requires pure and pristine crystals. Recently, the growth of pure single crystals of the spin-triplet superconductor UTe using a molten salt flux has been reported. In this study, we report research on vortices in UTe using such pure single crystals. As a result, in the magnetic field range of 15 T to 22 T, the critical current showed a maximum in temperature dependence, and a low-temperature region with a low critical current was observed deep in the superconducting state. This low critical current region matches the recently reported intermediate field superconducting phase. This suggests a weakening of the pinning force and a decrease in the critical current in the intermediate field superconducting phase.
Araki, Ryuhei; Yokoyama, Akira*; Kitazawa, Takafumi; Haga, Yoshinori; Hirose, Yusuke; Settai, Rikio*; Kimata, Motoi; Tokunaga, Yo
no journal, ,
no abstracts in English
Tokiwa, Yoshifumi; Opletal, P.; Sakai, Hironori; Yamamoto, Etsuji; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; et al.
no journal, ,
In unconventional superconductivity, magnetism is considered to be the origin of the superconducting interaction, and the relationship between magnetism and superconductivity is a central theme of research. UTe2 has attracted much attention due to its potential for reentrant superconductivity and spin-triplet superconductivity in magnetic fields. In this material, when a magnetic field is applied along the a-axis, a weak metamagnetism occurs near 6T due to Fermi surface instability. In the initial crystals synthesized by the vapor phase epitaxy, superconductivity disappeared in the magnetic field where metamagnetism was generated because 
= 1.6K and upper critical magnetic field 
= 6T, and superconductivity was not affected. In the pure single crystal synthesized by the molten salt flux method, =2.1K is 25% stronger than the initial Tc, while =12T is doubled. In this study, we revealed that this metamagnetism enhances .
Sakai, Hironori; Tokiwa, Yoshifumi; Kimata, Motoi; Awaji, Satoshi*; Sasaki, Takahiko*; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori
no journal, ,
We investigated the angular dependence of the superconducting phase diagram in UTe using magnetic fields up to 25 T. Precise measurements of ac susceptibility and resistivity were performed with a two-axis rotator. The results show that the low-field (LFSC) and high-field (HFSC) superconducting phases respond differently to field orientation. Notably, the HFSC phase emerges only within a narrow angle near the axis and disappears rapidly with tilting, suggesting strong anisotropy. We will discuss how the HFSC phase vanishes as the field tilts.
Sakai, Hironori; Tokiwa, Yoshifumi; Opletal, P.; Kimata, Motoi*; Awaji, Satoshi*; Sasaki, Takahiko*; Aoki, Dai*; Kambe, Shinsaku; Tokunaga, Yo; Haga, Yoshinori
no journal, ,
We have recently developed and optimized a molten salt flux method for growing high-purity single crystals of the superconductor UTe. The obtained crystals show a remarkably large residual resistivity ratio to the room temperature value and a small residual electronic contribution in specific heat well below . Using the high-quality single crystal of UTe, we have explored the superconducting phase diagram under magnetic fields along the hard magnetic -axis. Simultaneous electrical resistivity and AC magnetic susceptibility measurements discern low- and high-field SC (LFSC and HFSC, respectively) phases with contrasting field-angular dependence. Crystal quality increases the upper critical field of the LFSC phase, but the characteristic field of 
15 T, at which the HFSC phase appears, is always the same through the various crystals. A phase boundary signature is also observed inside the LFSC phase near the characteristic field of 15 T, indicating an intermediate SC phase characterized by small flux pinning forces.
