Quasiparticle characteristics of the weakly ferromagnetic Hund's metal MnSi

TL;DR

This study investigates the quasiparticle spectrum of MnSi, a Hund's metal with weak ferromagnetism, revealing how spin/orbital screening and magnetic order coexist and influence the electronic structure.

Contribution

It provides spectroscopic evidence of the interaction between Kondo-like screening and magnetic order in a Hund's metal, highlighting momentum-dependent quasiparticle behavior.

Findings

Observation of exchange-split bands below T_C

Development of quasiparticles upon cooling

Distinct temperature dependence of quasiparticle bands

Abstract

Hund's metals are multi-orbital systems with $3d$ or $4d$ electrons exhibiting both itinerant character and local moments, and they feature Kondo-like screenings of local orbital and spin moments, with suppressed coherence temperature driven by Hund's coupling $J_H$. They often exhibit magnetic order at low temperature, but how the interaction between the Kondo-like screening and long-range magnetic order is manifested in the quasiparticle spectrum remains an open question. Here we present spectroscopic signature of such interaction in a Hund's metal candidate MnSi exhibiting weak ferromagnetism. Our photoemission measurements reveal renormalized quasiparticle bands near the Fermi level with strong momentum dependence: the ferromagnetism manifests through possibly exchange-split bands (Q1) below $T_C$ , while the spin/orbital screenings lead to gradual development of quasiparticles (Q2) upon cooling. Our results demonstrate how the characteristic spin/orbital coherence in a Hund's metal could coexist and compete with the magnetic order to form a weak itinerant ferromagnet, via quasiparticle bands that are well separated in momentum space and exhibit distinct temperature dependence. Our results imply that the competition between the spin/orbital screening and the magnetic order in a Hund's metal bears intriguing similarity to the Kondo lattice systems.