Electronic Structure, Localization and Spin-State Transition in Cu-substituted FeSe: Fe$_{1-x}$Cu$_x$Se

TL;DR

This study uses density functional theory to explore how copper substitution affects the electronic, magnetic, and structural properties of FeSe, revealing a transition from itinerant to local moment magnetism and potential metal-insulator transition.

Contribution

It provides a detailed theoretical analysis of Cu substitution effects in FeSe, highlighting the transition to a spin-glass state and electronic localization phenomena.

Findings

Cu adopts a d10 configuration disrupting Fe electronic structure

Transition from weak moment to local moment magnet at x≈0.12

Possible metal-insulator transition due to Anderson localization

Abstract

We report density functional studies of the Fe$_{1-x}$Cu$_x$Se alloy done using supercell and coherent potential approximation methods. Magnetic behavior was investigated using the disordered local moment approach. We find that Cu occurs in a nominal $d^{10}$ configuration and is highly disruptive to the electronic structure of the Fe sheets. This would be consistent with a metal insulator transition due to Anderson localization. We further find a strong cross over from a weak moment itinerant system to a local moment magnet at $x \approx 0.12$. We associate this with the experimentally observed jump near this concentration. Our results are consistent with the characterization of this concentration dependent jump as a transition to a spin-glass.