IFW-Dresden, Institute for Solid State Research, Dresden, Germany.
J Phys Condens Matter. 2013 Apr 24;25(16):162204. doi: 10.1088/0953-8984/25/16/162204. Epub 2013 Apr 3.
(75)As NMR investigation of a single crystal of superconducting LiFeAs is presented. The Knight shift and the in situ ac susceptibility measurements as a function of temperature and external field are indicative of two superconducting (SC) transition temperatures, each of which is associated with its own upper critical field. Strikingly, the Knight shift maintains its normal state value over a temperature range in the SC state before it drops abruptly, being consistent with spin-singlet pairing. Together with our previous NMR study, the anomalous SC state featuring the constant Knight shift is attributed to the extremely sensitive SC properties of LiFeAs, probably stemming from its proximity to a critical instability.
（75）展示了对超导 LiFeAs 单晶的 NMR 研究。Knight 位移和原位交流磁化率随温度和外场的变化表明存在两个超导（SC）转变温度，每个温度都与自己的上临界场相关。引人注目的是，Knight 位移在 SC 状态下的正常状态值范围内保持不变，然后突然下降，与自旋单重态配对一致。结合我们之前的 NMR 研究，具有恒定 Knight 位移的异常 SC 状态归因于 LiFeAs 极其敏感的 SC 性质，可能源于其接近临界不稳定性。
