Inhomogeneous Superconducting State Probed by 125Te NMR on UTe2
Inhomogeneous Superconducting State Probed by 125Te NMR on UTe2
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DOI：
10.7566/jpsj.90.064709
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发表时间：
2021-06-15
影响因子：
1.7
通讯作者：
Aoki, Dai
中科院分区：
文献类型：
--
作者：
Nakamine, Genki;Kinjo, Katsuki;Aoki, Dai
UTe 2是最近发现的自旋三重态超导体的有希望的候选者。与传统的自旋单重态超导相反，自旋三重态超导具有自旋和角动量自由度。为了检测这些自由度，并获得坚实的证据自旋三重态超导在UTe 2，我们进行了Te-125-NMR测量，这是敏感的本地自旋磁化率在核网站。我们以前报道过，在低于超导转变温度Tc的核磁共振谱中，在平行于B的H方向上出现肩信号，并且在低磁场H下，在低于Tc的方向上，沿着B和c轴的Knight位移（分别为K-B和K-c）略有减小。尽管在5.5T以上K-c的降低消失，但在6.5T以下K-b的降低与H无关。为了阐明肩部信号的来源和K-B降低的痕迹，我们比较了当H平行于B和H平行于c时获得的Te-125-NMR谱，并测量了H平行于B的Te-125-NMR谱，直到14.5 T。对于平行于B的H观察到的肩信号的强度在类似于6 T处具有最大值，并且在高于10 T时消失，尽管超导电性通过chi（AC）测量确认，其可以在高达14.5 T（在本测量中的最大H）下存在。此外，SC状态下的K-b下降在7 T附近开始变小，在12.5 T时几乎为零。这表明SC自旋态随着H的加入而逐渐发生变化。同时，在平行于c的H中，在1 T下低于T-c时观察到不含肩信号的意外展宽，并且随着H的增加，该展宽迅速被抑制。我们根据核磁共振的测量结果，构造了H平行于B和H平行于c的H-T相图，并从理论上讨论了可能的SC态。我们认为，非均匀的SC状态的特点是扩大的NMR谱起源于自旋自由度。
UTe2 is a recently discovered promising candidate for a spin-triplet superconductor. In contrast to conventional spin-singlet superconductivity, spin-triplet superconductivity possesses spin and angular momentum degrees of freedom. To detect these degrees of freedom and obtain the solid evidence of spin-triplet superconductivity in UTe2, we have performed Te-125-NMR measurements, which are sensitive to the local spin susceptibility at a nuclear site. We previously reported that the shoulder signal appears in NMR spectra below the superconducting (SC) transition temperature T-c in H parallel to b, and a slight decrease in the Knight shift along the b and c axes (K-b and K-c, respectively) below T-c at a low magnetic field H. Although the decrease in K-c vanished above 5.5 T, the decrease in K-b was independent of H up to 6.5 T. To clarify the origin of the shoulder signal and the trace of the decrease in K-b, we compared the Te-125-NMR spectra obtained when H parallel to b and H parallel to c and measured the Te-125-NMR spectra for H parallel to b up to 14.5 T. The intensity of the shoulder signal observed for H parallel to b has a maximum at similar to 6 T and vanishes above 10 T, although the superconductivity is confirmed by the chi(AC) measurements, which can survive up to 14.5 T (maximum H in the present measurement). Moreover, the decrease in K-b in the SC state starts to be small around 7 T and almost zero at 12.5 T. This indicates that the SC spin state gradually changes with the application of H. Meanwhile, in H parallel to c, an unexpected broadening without the shoulder signals was observed below T-c at 1 T, and this broadening was quickly suppressed with increasing H. We construct the H-T phase diagram for H parallel to b and H parallel to c based on the NMR measurements and discuss possible SC states with the theoretical consideration. We suggest that the inhomogeneous SC state characterized by the broadening of the NMR spectrum originates from the spin degrees of freedom.