Paramagnetic electron-nuclear spin entanglement in HoCoZn

Kitazawa, Takafumi; Shimura, Yasuyuki*; Onimaru, Takahiro*; Tsuchida, Shun*; Kubo, Katsunori; Haga, Yoshinori; Sakai, Hironori; Tokiwa, Yoshifumi; Kambe, Shinsaku; Tokunaga, Yo

Physical Review Research (Internet), 8(2), p.023009_1 - 023009_14, 2026/04

https://doi.org/10.1103/bzvk-grrv

Self-reconstruction of order parameter in spin-triplet superconductor UTe

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

https://doi.org/10.1103/z8yx-yzdh

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.

Clear reduction in spin susceptibility and superconducting spin rotation for in the early-stage sample of spin-triplet superconductor UTe

Kitagawa, Shunsaku*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; 11 of others*

Journal of the Physical Society of Japan, 93(12), p.123701_1 - 123701_5, 2024/11

https://doi.org/10.7566/JPSJ.93.123701

Reinforcement of superconductivity by quantum critical fluctuations of metamagnetism in UTe

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

https://doi.org/10.1103/PhysRevB.109.L140502

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.

Quasi-2D Fermi surface in the anomalous superconductor UTe

Eaton, A. G.*; Weinberger, T. I.*; Popiel, N. J. M.*; Wu, Z.*; Hickey, A. J.*; Cabala, A.*; Pospil, J.*; Prokleka, J.*; Haidamak, T.*; Bastien, G.*; et al.

Nature Communications (Internet), 15, p.223_1 - 223_10, 2024/01

https://doi.org/10.1038/s41467-023-44110-4

High quality single crystal growth of a novel superconductor UTe; Improvement of and multiple superconducting phase diagram

Sakai, Hironori; Haga, Yoshinori

Kotai Butsuri, 58(10), p.529 - 536, 2023/10

We have succeeded to grow high-quality UTe single crystals with excess uranium through molten salt flux method. We have also studied the superconducting phase diagram using the high-quality crystal applying the fields up to 25 T along the magnetic hard axis.

Superconducting spin reorientation in spin-triplet multiple superconducting phases of UTe

Kinjo, Katsuki*; Fujibayashi, Hiroki*; Matsumura, Hiroki*; Hori, Fumiya*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; et al.

Science Advances (Internet), 9(30), p.2736_1 - 2736_6, 2023/07

https://doi.org/10.1126/sciadv.adg2736

Large reduction in the -axis knight shift on UTe with = 2.1 K

Matsumura, Hiroki*; Fujibayashi, Hiroki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Nakamura, Ai*; Shimizu, Yusei*; et al.

Journal of the Physical Society of Japan, 92(6), p.063701_1 - 063701_5, 2023/05

https://doi.org/10.7566/JPSJ.92.063701

Field induced multiple superconducting phases in UTe along hard magnetic axis

Sakai, 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

https://doi.org/10.1103/PhysRevLett.130.196002

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.

Anisotropic enhancement of lower critical field in ultraclean crystals of spin-triplet superconductor candidate UTe

Ishihara, Kota*; Kobayashi, Masayuki*; Imamura, Kumpei*; Konczykowski, M.*; Sakai, Hironori; Opletal, P.; Tokiwa, Yoshifumi; Haga, Yoshinori; Hashimoto, Kenichiro*; Shibauchi, Takasada*

Physical Review Research (Internet), 5(2), p.L022002_1 - L022002_6, 2023/04

https://doi.org/10.1103/PhysRevResearch.5.L022002

Lower superconducting critical fields of UTe have been determined. Orthorhombic UTe has magnetic easy axis along the -axis. We found perpendicular to showed anomalous enhancement. By comparing with anisotropy of upper critical fields, effect of magnetic fluctuations on superconductivity is suggested.