Symmetry of the Fermi surface and evolution of the electronic structure across the paramagnetic-helimagnetic transition in MnSi/Si(111)

TL;DR

This study uses angle-resolved photoemission spectroscopy to reveal the Fermi surface symmetry and electronic structure evolution in MnSi across its magnetic transition, highlighting nesting effects and quasiparticle behavior.

Contribution

It provides the first detailed mapping of the Fermi surface symmetry and its changes across the magnetic transition in MnSi, revealing nesting effects and quasiparticle dynamics.

Findings

Fermi surface shape fulfills nesting effects

Quasiparticle emission sharpens below T_C

Persistence of d-band splitting above T_C

Abstract

MnSi has been extensively studied for five decades, nonetheless detailed information on the Fermi surface (FS) symmetry is still lacking. This missed information prevented from a comprehensive understanding the nature of the magnetic interaction in this material. Here, by performing angle-resolved photoemission spectroscopy on high-quality MnSi films epitaxially grown on Si(111), we unveil the FS symmetry and the evolution of the electronic structure across the paramagnetic-helimagnetic transition at T$_C$ $\sim$ 40 K, along with the appearance of sharp quasiparticle emission below T$_C$. The shape of the resulting FS is found to fulfill robust nesting effects. These effects can be at the origin of strong magnetic fluctuations not accounted for by state-of-art quasiparticle self-consistent GW approximation. From this perspective, the unforeseen quasiparticle damping detected in the paramagnetic phase and relaxing only below T$_C$, along with the persistence of the d-bands splitting well above T$_C$, at odds with a simple Stoner model for itinerant magnetism, open the search for exotic magnetic interactions favored by FS nesting and affecting the quasiparticles lifetime.