Hund-enhanced electronic compressibility in FeSe and its correlation with T$_c$

TL;DR

This study investigates how Hund's correlations influence electronic compressibility in FeSe, revealing a link between enhanced compressibility regions and increased superconductivity, especially under pressure or doping.

Contribution

It demonstrates the role of Hund's metal physics in modulating electronic compressibility and its correlation with superconductivity in FeSe and monolayer FeSe.

Findings

Enhanced compressibility correlates with higher T_c.

Pressure and doping shift FeSe into regions of increased compressibility.

Results support Hund's correlations as a factor in superconductivity enhancement.

Abstract

We compute the compressibility of the conduction electrons in both bulk orthorhombic FeSe and monolayer FeSe on SrTiO$_3$ substrate, including dynamical electronic correlations within slave-spin mean-field + density-functional theory. Results show a zone of enhancement of the electronic compressibility crossing the interaction-doping phase diagram of these compounds in accord with previous simulations on iron pnictides and in general with the phenomenology of Hund's metals. Interestingly at ambient pressure FeSe is found slightly away from the zone with enhanced compressibility but moved right into it with hydrostatic pressure, while in monolayer FeSe the stronger enhancement region is realized on the electron-doped side. These findings correlate positively with the enhancement of superconductivity seen in experiments, and support the possibility that Hund's induced many-body correlations boost superconductive pairing when the system is at the frontier of the normal- to Hund's-metal crossover.