Effect of magnetic frustration on nematicity and superconductivity in Fe chalcogenides

TL;DR

This paper investigates how magnetic frustration in Fe chalcogenides influences nematicity and superconductivity, revealing unique magnetic interactions that explain pressure-dependent changes in superconducting temperature.

Contribution

It uncovers the role of magnetic frustration in Fe chalcogenides, explaining their distinct phase diagram and pressure effects on superconductivity, which differ from pnictides.

Findings

Magnetic frustration suppresses magnetic order but not nematic order.

Favors ferro-orbital order in the nematic phase.

Explains the nonmonotonic pressure dependence of $T_c$.

Abstract

Over the past few years Fe chalcogenides (FeSe/Te) have advanced to the forefront of Fe-based superconductors (FeBS) research. The most intriguing results thus far are for intercalated and monolayer FeSe, however experimental studies are still inconclusive. Yet, bulk FeSe itself remains an unusual case when compared with pnictogen-based FeBS, and may hold clues to understanding the more exotic FeSe-derivatives. The FeSe phase diagram is unlike the pnictides: the orthorhombic distortion, which is likely to be of a "spin-nematic" nature in numerous pnictides, is not accompanied by magnetic order in FeSe, and the superconducting transition temperature $T_{c}$ rises significantly with pressure before decreasing. In this paper we show that the magnetic interactions in chalcogenides, as opposed to pnictides, demonstrate unusual (and unanticipated) frustration, which suppresses magnetic, but not nematic order, favors ferro-orbital order in the nematic phase and can naturally explain the nonmonotonic pressure dependence of the superconducting critical temperature $T_{c}(P)$.