Optical evidence of the band reconstruction during the charge-density wave transition in annealed Kagome magnet FeGe

TL;DR

This study combines optical spectroscopy and first-principles calculations to reveal band structure reconstruction during the charge-density wave transition in annealed Kagome magnet FeGe, highlighting interactions among charge, lattice, and spin.

Contribution

It provides new insights into how annealing-induced lattice distortions influence band structure and magnetic properties in FeGe during CDW transitions.

Findings

Spectral weight transfer indicates band reconstruction during CDW transition.

Temperature-dependent spectral weight transfer correlates with magnetic properties.

Lattice distortion affects Fe 3d orbital energies and magnetic moments.

Abstract

In Kagome magnet FeGe, the coexistence of electron correlation, charge-density wave (CDW), and magnetism renders it ideal to study their interactions. Here, we combined the optical spectroscopy and the first-principles calculations to investigate the band structures of FeGe annealed at different temperatures. Our observations reveal that the sample annealed at 320C experienced dramatic change in optical conductivity following the CDW transition. Specifically, a substantial portion of the spectral weight (SW) in the low-energy region ( < 0.4 eV) was redistributed to the high-energy region (0.8 - 1.5 eV), suggesting a reconstruction of the band structure. The sample annealed at 560 C did not exhibit a CDW transition, but its SW transfer occurred progressively from 300 to 5 K. We noticed that: i) after the CDW transition, the sample annealed at 320 C showed similar tendency of SW transfer to that of the 560 C annealed sample; ii) the high-energy SW of both materials displayed a temperature dependence consistent with the magnetic roperties. Combining the first-principles calculations, we attribute the SW transfer to the band reconstruction triggered by the distortion of Ge1 atoms induced either by annealing at 560C or by the CDW transitions. This lattice distortion affects the energies of Fe 3d orbitals. Under the influence of Hund's rule coupling, the magnetic moment of Fe atoms is enhanced. Our findings elucidate the interactions among charge, lattice, and spin in FeGe, offering pivotal insights to modulate properties of this Kagome magnet.