通过原位双线圈互感测量和扫描隧道显微镜研究FeSe薄膜的正曲率临界场行为

高温超导研究过程中长期以来存在着一个极具争议的实验现象：正曲率的H*-T关系(H*是使得样品的电阻在温度为T时消失的外磁场)。实验上和理论上对该行为起源的认识始终未达成同一。而临界场决定了配对势和库珀对尺寸，因此对该反常的研究收到了众多关注。本项目将以表面吸附了碱金属K原子的多层FeSe薄膜为研究对象，结合原位双线圈互感技术、原位四探针技术和扫描隧道显微镜/谱技术，同时从宏观和微观两方面来研究该临界场行为，对经常出现于二维超导体中的正曲率H*-T关系曲线的正确理解提供重要实验指导。同时，在整个“穹顶”型超导相图范围内，通过对比不同超导相关参数(超导能隙、超流密度、配对势、库珀对尺寸等)，明确影响超导转变温度的重要因素，为最终理解高温超导机制提供重要实验证据。

A very controversial phenomenon observed in researches on high temperature superconductivity is the appearance of a strong upward curvature in critical field H*-T, where H* denotes the field which makes the sample lost its resistance at temperature T. The academic circles have different views on this anomaly. Since critical field determines the strength of the pairing potential and the value of the coherence length, this anomalous behavior thus stimulates enormous attempts. In this project, by using situ two-coil mutual inductance technique, four-point probe technique and scanning tunneling microscopy, the influence of temperature and doping on a critical transition field in potassium adsorbed multilayer FeSe films will be studied from macroscopic and microscopic scale. This will provide crucial guidance for the understanding of this positive curve in critical field that frequently appears in two dimensional superconductors. Meanwhile, through a comparative analysis of superconducting transition temperature and other energy scales that are relevant for the superconducting state, such as superconducting energy gap, superfluid stiffness, pair protentional, and the size of Cooper pair, the most important factors that affect Tc can be clarified, which is a crucial step towards the mechanistic understanding of high-Tc superconductivity.