Mass enhancements and band shifts in strongly hole overdoped Fe-based pnictide superconductors: KFe$_2$As$_2$ and CsFe$_2$As$_2$

TL;DR

This study investigates the mass renormalizations and band shifts in highly hole-overdoped Fe-based pnictide superconductors KFe$_2$As$_2$ and CsFe$_2$As$_2$, revealing insights into their electronic correlations and proximity to quantum criticality.

Contribution

It provides a phenomenological analysis combining ARPES data and GGA calculations to understand band shifts and correlations in heavily hole-doped Fe-based superconductors.

Findings

Increased Sommerfeld coefficient from K122 to Cs122 due to low-energy boson coupling.

No significant increase in correlations for Cs122 compared to K122.

Empirical VHS positions suggest weaker correlations in Cs122, consistent with magnetic susceptibility data.

Abstract

The interplay of high and low-energy mass renormalizations with band-shifts reflected by the positions of van Hove singularities (VHS) in the normal state spectra of the highest hole-overdoped and strongly correlated AFe$_2$As$_2$ (A122) with A = K, Cs is discussed phenomenologically based on ARPES data and GGA band-structure calculations with full spin-orbit coupling. The big increase of the Sommerfeld coefficient $\gamma$ from K122 to Cs122 is ascribed to an enhanced coupling to low-energy bosons in the vicinity of a quantum critical point to an unknown, yet incommensurate phase different from the commensurate Mott one. We find no sizeable increase in correlations for Cs122 in contrast to F. Eilers et al., PRL v. 116, 237003 (2016) [3]. The empirical (ARPES) VHS positions as compared with GGA-predictions point even to slightly weaker correlations in Cs122 in accord with low-$T$ magnetic susceptibility $\chi(T)$ data and a decreasing Wilson ratio $\propto \chi(0)/\gamma$.