Topological Dirac semimetal phase in the iron-based superconductor Fe(Te,Se)

TL;DR

This paper reports the discovery of a topological Dirac semimetal phase in the iron-based superconductor Fe(Te,Se), combining experimental evidence and theoretical calculations, and highlighting its potential for topological superconductivity.

Contribution

It provides the first evidence of a TDS phase in Fe(Te,Se), linking topological states with high-temperature superconductivity in this material.

Findings

Spin-polarized surface states overlapping with bulk states

Linear magnetoresistance observed from 6 T

Theoretical confirmation of TDS phase

Abstract

Topological Dirac semimetals (TDSs) exhibit bulk Dirac cones protected by time reversal and crystal symmetry, as well as surface states originating from non-trivial topology. While there is a manifold possible onset of superconducting order in such systems, few observations of intrinsic superconductivity have so far been reported for TDSs. We observe evidence for a TDS phase in FeTe$_{1-x}$Se$_x$ ($x$ = 0.45), one of the high transition temperature ($T_c$) iron-based superconductors. In angle-resolved photoelectron spectroscopy (ARPES) and transport experiments, we find spin-polarized states overlapping with the bulk states on the (001) surface, and linear magnetoresistance (MR) starting from 6 T. Combined, this strongly suggests the existence of a TDS phase, which is confirmed by theoretical calculations. In total, the topological electronic states in Fe(Te,Se) provide a promising high $T_c$ platform to realize multiple topological superconducting phases.