Direct observation of the energy gain underpinning ferromagnetic superexchange in the electronic structure of CrGeTe$_3$

TL;DR

This study reveals how specific orbital interactions and electronic state changes drive ferromagnetic ordering in CrGeTe3, highlighting the interplay between localized and itinerant electrons through temperature-dependent spectroscopic analysis.

Contribution

It provides the first direct observation of energy changes associated with superexchange in CrGeTe3 using advanced spectroscopic techniques.

Findings

Covalent bonding between Te 5p and Cr eg orbitals drives ferromagnetism.

Cr t2g states carry the majority of the spin moment.

Bandwidth and lifetime of t2g states increase in the ordered phase.

Abstract

We investigate the temperature-dependent electronic structure of the van der Waals ferromagnet, CrGeTe$_3$. Using angle-resolved photoemission spectroscopy, we identify atomic- and orbital-specific band shifts upon cooling through ${T_\mathrm{C}}$. From these, together with x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements, we identify the states created by a covalent bond between the Te ${5p}$ and the Cr ${e_g}$ orbitals as the primary driver of the ferromagnetic ordering in this system, while it is the Cr ${t_{2g}}$ states that carry the majority of the spin moment. The ${t_{2g}}$ states furthermore exhibit a marked bandwidth increase and a remarkable lifetime enhancement upon entering the ordered phase, pointing to a delicate interplay between localized and itinerant states in this family of layered ferromagnets.