2026-07-30 神戸大学
©2026 The Author(s)
＜関連情報＞
- https://www.kobe-u.ac.jp/ja/news/article/20260730-68160/
- https://journals.jps.jp/doi/10.7566/JPSJ.95.074711
UBe13におけるフルギャップスピン三重項超伝導状態のNMRによる証拠 NMR Evidence for Full-Gap Spin-Triplet Superconducting State in UBe13
Shoko Minami, Haruki Matsuno, Kyohei Morita, Rintaro Matsuki, Hisashi Kotegawa, Hisatomo Harima, …
Journal of the Physical Society of Japan Published: June 26, 2026
DOI:https://doi.org/10.7566/JPSJ.95.074711
Abstract
The nature of the superconducting (SC) order parameter in the heavy-fermion superconductor UBe13 has been a subject of intense debate for decades. Here, we report on comprehensive 9Be-NMR measurements performed on a single crystal of UBe13 to investigate the quasiparticle spin susceptibility and the nuclear spin–lattice relaxation rate 1/T1 under magnetic fields up to 2 T. Our results reveal several key features: (i) the Knight shift (KS) remains unchanged below Tc down to a characteristic temperature T* ≈ 0.7 K, indicating a parallel-spin pairing state where the d-vector is reoriented by the external field (d ⊥ H); (ii) below T*, the KS exhibits an anisotropic partial reduction along all major cubic axes, which provides smoking-gun evidence for a spin-triplet SC state; and (iii) the 1/T1 data are well described by a multi-band, fully gapped model, effectively ruling out the presence of nodal structures. By comparing the experimental anisotropic reduction of the spin susceptibility with group-theoretical candidates, we identify a unitary mixed state of A1u + αEu(1) symmetry (with −0.11 < α < −0.06) as the most plausible order parameter. These findings are consistent with a multi-band, fully gapped, spin-triplet topological superconducting state in UBe13. Furthermore, the observed 1/T1 at low temperatures is significantly suppressed compared to the conventional Caroli–de Gennes–Matricon (CdGM) mechanism, indicating the emergence of the quantum limit in vortex cores.
