Fermi surface expansion above critical temperature in a Hund ferromagnet

TL;DR

This study reveals that in Hund's ferromagnets, the Fermi surface expands above the Curie temperature due to momentum-space Hund's physics and ferromagnetic fluctuations, leading to electronic structure changes.

Contribution

It demonstrates that Hund's physics causes Fermi surface expansion and electronic structure reconstruction above the magnetic transition temperature.

Findings

Fermi surface expands above $T_C$ in Hund's ferromagnets.

Momentum-dependent electron correlations induce electronic structure changes.

Ferromagnetic fluctuations drive the observed phenomena.

Abstract

Using a cluster extension of the dynamical mean-field theory, we show that strongly correlated metals subject to Hund's physics exhibit significant electronic structure modulations above magnetic transition temperatures. In particular, in a ferromagnet having a large local moment due to Hund's coupling (Hund's ferromagnet), the Fermi surface expands even above the Curie temperature ($T_{\rm C}$) as if a spin polarization occurred. Behind this phenomenon, effective ``Hund's physics'' works in momentum space, originating from ferromagnetic fluctuations in the strong coupling regime. The resulting significantly momentum-dependent (spatially nonlocal) electron correlations induce an electronic structure reconstruction involving a Fermi-surface volume change and a redistribution of the momentum-space occupation. Our finding will give a deeper insight into the physics of Hund's ferromagnets above $T_{\rm C}$.