Charge Dynamics of an Unconventional Three-Dimensional Charge Density Wave in Kagome FeGe
Shaohui Yi, Zhiyu Liao, Qi Wang, Haiyang Ma, Jianpeng Liu, Xiaokun Teng, Bin Gao, Pengcheng Dai, Yaomin Dai, Jianzhou Zhao, Yanpeng Qi, Bîng Xu, Xianggang Qiu
Abstract
We report on the charge dynamics of kagome FeGe, an antiferromagnet with a charge density wave (CDW) transition at T_{CDW}≃105 K, using polarized infrared spectroscopy and band structure calculations. We reveal pronounced optical anisotropy along the a and c axis, as well as an unusual response associated with three-dimensional CDW order. Above T_{CDW}, there is a notable transfer of spectral weight (SW) from high to low energies, promoted by the magnetic splitting-induced shift in bands. Across the CDW transition, we observe a sudden SW transfer from low to high energies over a broad range, along with the emergence of new excitations around 1200 cm^{-1}. These results contrast with observations from other kagome metals like CsV_{3}Sb_{5}, where the nesting of VHSs leads to a clear CDW gap feature. Instead, our findings can be accounted for by a 2×2×2 CDW ground state driven by a first-order structural transition involving large partial Ge1 dimerization. Our Letter thus unveils a complex interplay among structure, magnetism, and charge order, offering valuable insights for a comprehensive understanding of CDW order in FeGe.