Evidence for interfacial superconductivity in a bi-collinear antiferromagnetically ordered FeTe monolayer on a topological insulator

TL;DR

This study demonstrates interfacial superconductivity in ultrathin FeTe monolayers on topological insulators, revealing coexistence with antiferromagnetic order and suggesting new avenues for exploring exotic phases in heterostructures.

Contribution

It provides atomic-scale evidence of superconductivity coexisting with antiferromagnetic order in FeTe monolayers on topological insulators, a novel finding in the field.

Findings

Superconducting gap observed at Tc ~ 6 K in FeTe monolayers

Superconductivity coexists with bicollinear AFM order at the atomic scale

Ultrathin FeTe layers exhibit superconductivity unlike bulk FeTe

Abstract

The discovery of high-temperature superconductivity in Fe-based compounds [1,2] has triggered numerous investigations on the interplay between superconductivity and magnetism [3] and, more recently, on the enhancement of transition temperatures through interface effects [4]. It is widely believed that the emergence of optimal superconductivity is intimately linked to the suppression of long-range antiferromagnetic (AFM) order, although the exact microscopic picture of this relationship remains elusive [1] due to the lack of data with atomic spatial resolution [5-7]. Here, we present a spin-polarized scanning tunneling spectroscopy (SP-STS) study of ultrathin FeTe$_{1-x}$Se$_x$ (x = 0, 0.5) films grown on prototypical Bi-based bulk topological insulators. Surprisingly, we find an energy gap at the Fermi level indicating superconducting correlations up to Tc ~ 6 K for one unit cell thin FeTe layers grown on Bi2Te3 substrates, in contrast to the non-superconducting FeTe bulk compound [8]. Moreover, SP-STS reveals that the energy gap spatially coexists with bicollinear AFM order. This finding opens novel perspectives for theoretical studies of competing orders in Fe-based superconductors as well as for experimental investigations of exotic phases in heterostructures of topological insulators and superconducting layers.