Observation and characterization of the zero energy conductance peak in the vortex core state of FeTe$_{0.55}$Se$_{0.45}$

TL;DR

This study investigates zero energy conductance peaks in vortex cores of FeTe$_{0.55}$Se$_{0.45}$, revealing complex behaviors and potential Majorana modes relevant for quantum computing, with findings on their dependence on magnetic field and temperature.

Contribution

It provides detailed experimental characterization of zero energy modes in FeTe$_{0.55}$Se$_{0.45}$ vortex cores, expanding understanding of their nature and conditions.

Findings

Zero bias conductance peaks observed in some vortices.

ZBCP probability decreases with increasing magnetic field.

ZBCP weakens and disappears around 4 K.

Abstract

The search for the Majorana fermions in condensed matter physics has attracted much attention, partially because they may be used for the fault-tolerant quantum computation. It has been predicted that the Majorana zero mode may exist in the vortex core of topological superconductors. Recently, many iron-based superconductors are claimed to exhibit a topologically nontrivial surface state, including Fe(Te,Se). Some previous experiments through scanning tunneling microscopy (STM) have found zero-bias conductance peaks (ZBCP) within the vortex cores of Fe(Te,Se). However, our early experimental results have revealed the Caroli-de Gennes-Matricon (CdGM) discrete quantum levels in about 20% vortices. In many other vortices, we observed a dominant peak locating near zero bias. Here we show further study on the vortex core state of many more vortices in FeTe$_{0.55}$Se$_{0.45}$. In some vortices, if we take a certain criterion of bias voltage window near zero energy, we indeed see a zero energy mode. Some vortices exhibit zero energy bound state peaks with relatively symmetric background, which cannot be interpreted as the CdGM discrete states. The probability for vortices showing the ZBCP lowers down with the increase of magnetic field. Meanwhile it seems that the presence and absence of the ZBCP has no clear relationship with the Te/Se ratio on the surface. Temperature dependence of the spectra reveals that the ZBCP becomes weakened with increasing temperature and disappears at about 4 K. Our results provide a confirmed supplementary to the early claimed zero energy modes within the vortex cores of Fe(Te,Se). Detailed characterization of these zero energy modes versus magnetic field, temperature and spatial distribution of Te/Se will help to clarify its origin.