Multiple topological states in iron-based superconductors

TL;DR

This paper demonstrates the coexistence of multiple topological states and superconductivity in iron-based superconductors, revealing their potential as platforms for high-temperature topological superconductivity and Majorana bound states.

Contribution

It identifies and characterizes topological insulator and Dirac semimetal bands near the Fermi level in iron-based superconductors, showing their tunability and coexistence with superconductivity.

Findings

Topological insulator and Dirac semimetal bands are present near the Fermi level.

These topological states can be tuned via doping.

Superconductivity coexists with multiple topological states in these materials.

Abstract

Topological insulators and semimetals as well as unconventional iron-based superconductors have attracted major recent attention in condensed matter physics. Previously, however, little overlap has been identified between these two vibrant fields, even though the principal combination of topological bands and superconductivity promises exotic unprecedented avenues of superconducting states and Majorana bound states (MBSs), the central building block for topological quantum computation. Along with progressing laser-based spin-resolved and angle-resolved photoemission spectroscopy (ARPES) towards high energy and momentum resolution, we have resolved topological insulator (TI) and topological Dirac semimetal (TDS) bands near the Fermi level ($E_{\text{F}}$) in the iron-based superconductors Li(Fe,Co)As and Fe(Te,Se), respectively. The TI and TDS bands can be individually tuned to locate close to $E_{\text{F}}$ by carrier doping, allowing to potentially access a plethora of different superconducting topological states in the same material. Our results reveal the generic coexistence of superconductivity and multiple topological states in iron-based superconductors, rendering these materials a promising platform for high-$T_{\text{c}}$ topological superconductivity.