Time Reversal Symmetry Breaking in the Fe-Chalcogenide Superconductors

TL;DR

This paper investigates how time-reversal symmetry breaking occurs in Fe-chalcogenide superconductors, revealing the interplay of topology, magnetism, and superconductivity, and its implications for topological phenomena and Majorana fermions.

Contribution

It provides experimental evidence of time-reversal symmetry breaking and ferromagnetism in FeSeTe superconductors using high-resolution photoemission.

Findings

Observation of a second gap at the Dirac point indicating symmetry breaking

Evidence of intrinsic ferromagnetism in the surface layer

Potential for exotic topological phenomena due to combined effects

Abstract

Topological superconductivity has been sought for in a variety of heterostructure systems, the interest being that a material displaying such a phenomenon could prove to be the ideal platform to support Majorana fermions, which in turn could be the basis for advanced qubit technologies. Recently the high Tc family of superconductors, $FeSe_{x}Te_{1-x}$, have been shown to exhibit the property of topological superconductivity and further, evidence has been found for the presence of Majorana fermions. We have studied the interplay of topology, magnetism and superconductivity in the $FeSe_{x}Te_{1-x}$ family using high-resolution laser-based photoemission. At the bulk superconducting transition, a gap opens at the chemical potential as expected. However, a second gap is observed to open at the Dirac point in the topological surface state. The associated mass acquisition in the topological state points to time-reversal symmetry breaking, probably associated with the formation of ferromagnetism in the surface layer. The presence of intrinsic ferromagnetism combined with strong spin-orbit coupling provides an ideal platform for a range of exotic topological phenomena.