FeSe/SrTiO3界面超导的调控研究

In 2012, Chinese scientists discovered that one unit cell FeSe film grown on SrTiO3 substrate has a superconducting gap nearly ten times the gap value of the bulk, showing a signature of superconductivity above the liquid nitrogen temperature (77 K). However, up to date there is no direct proof, such as zero resistance and Meissner effect, to show unambiguously that the FeSe/SrTiO3 interface enters the macroscopic superconducting state at liquid nitrogen temperature. In this project, we plan to modulate the superconductivity of FeSe/ SrTiO3 interface by doping, field effect and dual interface effect (fabricating sandwiched structures) , and to explore FeSe/SrTiO3 interface superconductivity at liquid nitrogen temperature by in-situ scanning tunneling spectroscopy and in-situ transport. Moreover, we will fabricate atomically sharp topological insulator/superconductor interface by epitaxially growing topological insulators such as Bi2Se3 on this single layer FeSe film to search for Majorana Fermions. This project will represent a significant progress in the investigations of the superconducting mechanism and searching for novel high Tc superconductors and topological superconductors.

2012年，我国科学家率先发现外延于SrTiO3衬底上单层FeSe薄膜具有十倍于体态值的超导能隙，意味着其超导转变温度可能超过液氮温度(77 K)。然而，至今还没有直接的实验证据，即零电阻和绝对抗磁性，确切证实FeSe/SrTiO3在液氮温区就进入宏观超导态。在本项目中，我们将利用掺杂、场效应、和人工构建三明治结构(双界面)等方法对FeSe/SrTiO3界面超导性质进行调控，通过原位扫描隧道显微镜和原位输运测量对其超导特性进行表征，期望获得超过液氮温区的界面超导体系。同时，我们还将在单层FeSe表面外延生长Bi2Se3族拓扑绝缘体材料，获得原子级平整、排列有序的拓扑绝缘体/超导异质结构，探索拓扑超导体和Majorana费米子。本项目的实施将对研究高温超导机理和探索高温超导材料以及拓扑超导体产生巨大推进作用。

在本项目执行过程中，按照申请书中研究计划进行了碱金属掺杂和SrTiO3衬底氧空位调控下FeSe/SrTiO3界面超导性质的表征和调控，发现电荷掺杂和SrTiO3表面Ti-O振动模对FeSe电子配对具有重要作用，并且界面电荷转移和Ti-O振动模与表面氧空位浓度密切相关。基于以上认识，我们继续探索超导层/氧化物界面的超导特性，发现了FeSe/MgO和FeSe/GaO2界面增强超导体系。我们还利用SrTiO3衬底模板作用制备了四方相CoSe和CoSb薄膜，结合谱学和抗磁性测试表明CoSb/SrTiO3可能是新的超导体系。.以上相关工作为理解界面高温超导机制和探索新的界面超导体系提供了丰富的实验依据。