Superconducting fluctuations in FeSe investigated by precise torque magnetometry

We investigated the superconducting fluctuation in FeSe, which is assumed to be located in the BCS-BEC crossover region, via magnetic torque measurements. In our method, the absolute cantilever displacement is measured by detecting the interference intensity of the Fabry-Perot cavity formed between the cantilever and optical fiber. Our findings are different from the results of previous torque magnetometry studies using a piezoresistive cantilever; the "giant" fluctuation diamagnetism related to the BCS-BEC crossover does not exist. Instead, a considerably smaller fluctuation signal originating from the vortex liquid was observed that showed qualitatively similar behavior to that in cuprate superconductors. We also discuss the inconsistency between our torque data and the existence of a pseudogap proposed by an NMR experiment.

我们通过磁扭矩测量研究了FeSe中的超导涨落，FeSe被认为处于BCS - BEC渡越区域。在我们的方法中，通过检测悬臂和光纤之间形成的法布里 - 珀罗腔的干涉强度来测量悬臂的绝对位移。我们的发现与之前使用压阻悬臂的扭矩磁强计研究结果不同；与BCS - BEC渡越相关的“巨大”涨落抗磁性并不存在。相反，观察到一个源自涡旋液体的相当小的涨落信号，其行为在性质上与铜酸盐超导体中的类似。我们还讨论了我们的扭矩数据与核磁共振实验所提出的赝能隙存在之间的不一致性。