STM study on the vortex states and Majorana zero-modes in FeSe-based high-Tc superconductors

Abstract

The Majorana fermions/quasi-particles obey non-Abelian statistics and play an essential role in topological quantum computing. Theoretically, they can be realized as a zero-energy excitation in the vortex core of topological superconductors, called Majorana zero mode (MZM). However, the coexisting low-energy bound states in vortex cores often bring difficulties for identifying MZM. In this review, we summarized recent STM studies on the vortex states of electron-doped FeSe-based superconductors such as (Li,Fe)OHFeSe and single-layer FeSe/SrTiO3. Zero-bias conductance peaks (ZBCP) are observed in the unpinned vortex cores of (Li,Fe)OHFeSe. It displays nearly quantized conductance and distinct spatial distributions with respect to nonzero bound states, which indicates their nontrivial origin. Meanwhile, single-layer FeSe/SrTiO3 film only has conventional Caroli-de Gennes-Matricon (CdGM) bound states without zero-energy mode, reflecting the characteristics of s-wave superconductor. These results not only provide strong evidence of MZM, but also shed light on its origin in FeSe-based superconductors.