电子型FeSe基高温超导体的磁通束缚态与Majorana零能模

作为凝聚态物理中一类新奇准粒子态,Majorana零能模(Majorana zero mode)由于可用来实现拓扑量子计算而成为当前的研究热点.理论预言,Majorana零能模可作为特殊的束缚态出现在一些拓扑超导体的磁通涡旋中.但实际超导体磁通中还可能存在其他低能束缚态或杂质态,这给Majorana零能模的辨别和具体应用带来了困难.目前实验上寻找合适的拓扑超导体系、分辨出清晰的Majorana零能模仍然是十分迫切的.本文主要介绍最近利用高能量分辨的扫描隧道显微镜,对电子掺杂铁硒类超导体(Li,Fe)OHFeSe和单层FeSe/SrTiO3磁通态进行的研究.实验上在前者的自由磁通中观测到清晰的零能模,并进一步测量到Majorana零能模的重要特征—量子化电导.而在后者磁通中只发现常规Caroli-de Gennes-Matricon(CdGM)束缚态,反映出s波对称性的特征.这系列实验既为Majorana零能模物性的进一步研究提供了合适平台,也为澄清铁基超导体中拓扑超导电性的来源提供了线索.

Vortex bound states and Majorana zero mode in electrondoped FeSe-based high-temperature superconductor

As a novel quantum state in condensed matter physics,Majorana zero mode has become a popular research topic at present because of its potential value in topological quantum computing.Theory predicts that Majorana zero mode appears in the vortex core of the topological superconductor as a unique bound state.However,due to various factors such as the existence of conventional low energy bound states or impurity states,it is difficult to identify the Majorana zero mode and to put it into the specific applications.Nowadays,it is still urgent to find a suitable topological superconducting system and identify the clean Majorana zero mode in experiment.In this paper,we study the vortex states of electron-doped iron-selenium-based superconductors(Li,Fe)OHFeSe and single-layer FeSe/SrTiO3 with extremely high energy resolution STM.There exists a robust and clean Majorana zero mode in the free vortex core of(Li,Fe)OHFeSe,which has the quantized conductance.As for single-layer FeSe/SrTiO3 film,it has only conventional Caroli-de Gennes-Matricon(CdGM)bound states without zero energy mode.These experimental results provide a suitable platform for further studying the physical properties of Majorana zero mode,and also shed light on the source of topological superconductivity in iron-based superconductors.