In this work, combined with the optical spectroscopy and the first-principles calculations, we investigated the effect of lattice distortion on the band structure and magnetism of FeGe annealed at different temperatures. Our observations reveal that the sample annealed at $320{}^{\circ }\mathrm{C}$ experienced dramatic change in optical conductivity following the charge-density-wave (CDW) transition. Specifically, a substantial portion of the spectral weight (SW) in the low-energy region $(<0.4\mathrm{eV})$ was redistributed to the high-energy region $(0.8\sim 1.5\mathrm{eV})$, suggesting a reconstruction of the band structure. The sample annealed at $560{}^{\circ }\mathrm{C}$ did not exhibit a CDW transition, but it exhibited the same tendency of SW transfer from 300 to 5 K progressively. Through the first-principles calculations, we ascribed the band reconstruction to Ge1 atoms' dimerization along the $c$ axis and analyzed its affection to the magnetism. On the other hand, even though the CDW transition is absent in $560{}^{\circ }\mathrm{C}$ annealed sample, the high-temperature annealing induced lattice distortion, resulting in the same optical properties, further emphasized that the band reconstruction and the enhanced magnetism primarily come from the displacement of Ge1 atoms.

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• Charge density waves
• Kagome metal
• Density functional theory
• Infrared spectroscopy