  Kagome materials provide a promising platform to explore intriguing
correlated phenomena including magnetism, charge density wave (CDW), and
nontrivial band topology. Recently, a CDW order was observed in
antiferromagnetic kagome metal FeGe, sparking enormous research interests in
intertwining physics of CDW and magnetism. Two of the core questions are (i)
what are the driving forces of the CDW transition in FeGe and (ii) whether
magnetism play a critical role in the transition. Such questions are critical
as conventional mechanisms of van Hove singularities and Fermi surface nesting
fail to explain the stable pristine phase, as well as the role of magnetism.
Here, supported by density functional theory and tight-binding models, we
unravel the triple-well CDW energy landscape of FeGe, indicating that both the
pristine and CDW phases are locally stable. We point out that an entire
downward shift of Ge band, instead of the previously proposed Fe bands,
competes with the lattice distortion energy, driving the triple-well CDW
transition. It is indeed a cooperation between the Peierls-like effect and the
Fermi energy pinning phenomenon, which is distinct from the conventional
Peierls effect that drives a double-well transition. Moreover, we demonstrate
that the antiferromagnetic order also plays a critical role in driving the CDW
transition, through weakening the Fe-Ge hybridization by exchange splitting and
lowering the position of Ge-bands with respect to the Fermi energy. Our work
thus not only deepens the understanding of the CDW mechanism in FeGe, but also
indicates an intertwined connection between the emergent magnetism and CDW in
kagome materials.
