Recently, a first-order phase transition associated with charge density wave (CDW) has been observed at low temperatures in intermetallic compound BaFe2Al9. However, this transition is absent in its isostructural sister compound BaCo2Al9. Consequently, an intriguing question arises as to the underlying factors that differentiate BaFe2Al9 from BaCo2Al9 and drive the CDW transition in BaFe2Al9. Here, we set out to address this question by conducting a comparative \emph{ab initio} study of the electronic structures, lattice dynamics, \textcolor{black}{and electron-phonon interactions} of their high-temperature phases. We find that both compounds are dynamically stable with similar phonon dispersions. The electronic structure calculations reveal that both compounds are nonmagnetic metals; however, they exhibit distinct band structures around the Fermi level. In particular, BaFe2Al9 exhibits a higher density of states at the Fermi level with dominant partially filled Fe-3d states and a more intricate Fermi surface. This leads to an electronic instability of BaFe2Al9 toward the CDW transition, which is manifested by the diverged electronic susceptibility at the CDW wave vector qCDW=(0.5, 0, 0.3), observable in both the real and imaginary parts. Conversely, BaCo2Al9 does not display such behavior, aligning well with experimental observations. Although the electron-phonon interactions in BaFe2Al9 surpass those in BaCo2Al9 by two orders of magnitude, the strength is relatively weak at the CDW wave vector, suggesting that the CDW in BaFe2Al9 is primarily driven by electronic factors.
@article{arxiv.2410.22734,
title = {Origin of the charge density wave state in BaFe$_2$Al$_9$},
author = {Yuping Li and Mingfeng Liu and Jiangxu Li and Jiantao Wang and Junwen Lai and Dongchang He and Ruizhi Qiu and Yan Sun and Xing-Qiu Chen and Peitao Liu},
journal= {arXiv preprint arXiv:2410.22734},
year = {2024}
}