今回測定したUTe2は、その高い上部臨界磁場 Hc2や磁場・圧力によって超伝導多重相があらわれることから、発見当初からスピン三重項超伝導体の有力な候補とされてきました。わたしたちはこれまでに核磁気共鳴（NMR）測定によって、UTe2がスピン三重項状態である確証を得ています。一方、初期段階のサンプルと超高純度サンプルの間には結果の食い違いがありました。具体的には、超高純度サンプルではa軸磁場においてスピン磁化率が大幅に減少するのに対し、初期段階のサンプルではそのような減少は観測されていません。このスピン磁化率の減少は、スピン三重項超伝導体における秩序変数である d ベクトル、超伝導スピンと垂直方向のベクトルが磁場方向の成分を持っていることを示していて、結果の違いは超伝導対称性が違うことを示唆しています。この結果の食い違いは、i)小さな磁場による超伝導スピンの回転、ii)微小な不純物や欠陥によるスピン磁化率の減少の抑制、またはiii)超伝導にならない部分からの信号の観測が原因と考えていました。
@article{S.Kitagawa_JPSJ_2024,
title = {Clear Reduction in Spin Susceptibility and Superconducting Spin Rotation for H || a in the Early-Stage Sample of Spin-Triplet Superconductor UTe2},
author = {S Kitagawa and K Nakanishi and H Matsumura and Y Takahashi and K Ishida and Y Tokunaga and H Sakai and S Kambe and A Nakamura and Y Shimizu and D Li and F Honda and A Miyake and D Aoki},
url = {https://doi.org/10.7566/JPSJ.93.123701
https://arxiv.org/abs/2411.02698},
doi = {10.7566/JPSJ.93.123701},
year = {2024},
date = {2024-11-01},
urldate = {2024-11-01},
journal = {Journal of the Physical Society of Japan},
volume = {93},
pages = {123701},
abstract = {We report the re-measurement of the a-axis spin susceptibility component in an early-stage sample of the spin-triplet superconductor UTe2 with the transition temperature of TSC = 1.6 K. Using Knight-shift measurements along the b axis and at a 10-degree tilt from the b axis towards the a axis, we accurately determined the a-axis component without directly measuring the a-axis Knight shift. Our results reveal a decrease of approximately 3% in the a-axis spin susceptibility in the superconducting state under a-axis magnetic field μ0Ha ∼ 0.1 T, indicating that the spin susceptibility decreases similarly in both early-stage and ultraclean samples with TSC = 2.1 K. The previously reported absence of the reduction in Knight shift is attributed to the missing of signal from the superconducting region and to the detection of residual signals from the non-superconducting region instead. We also found that the decrease in the a-axis spin susceptibility is immediately suppressed with increasing the a-axis magnetic field and is estimated to be completely suppressed at around 1.5 T due to superconducting spin rotation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the re-measurement of the a-axis spin susceptibility component in an early-stage sample of the spin-triplet superconductor UTe2 with the transition temperature of TSC = 1.6 K. Using Knight-shift measurements along the b axis and at a 10-degree tilt from the b axis towards the a axis, we accurately determined the a-axis component without directly measuring the a-axis Knight shift. Our results reveal a decrease of approximately 3% in the a-axis spin susceptibility in the superconducting state under a-axis magnetic field μ0Ha ∼ 0.1 T, indicating that the spin susceptibility decreases similarly in both early-stage and ultraclean samples with TSC = 2.1 K. The previously reported absence of the reduction in Knight shift is attributed to the missing of signal from the superconducting region and to the detection of residual signals from the non-superconducting region instead. We also found that the decrease in the a-axis spin susceptibility is immediately suppressed with increasing the a-axis magnetic field and is estimated to be completely suppressed at around 1.5 T due to superconducting spin rotation.
