Kavli Affiliate: Yi Zhou
| First 5 Authors: Rui Lou, Yumeng Zhang, Erjian Cheng, Xiaolong Feng, Alexander Fedorov
| Summary:
The origin of the charge order in kagome lattice materials has attracted
great interest due to the unique electronic structure features connected to
kagome networks and the interplay between electron and lattice degrees of
freedom. Recently, compounds with composition $Ln$Nb$_6$Sn$_6$ ($Ln$ = Ce-Nd,
Sm, Gd-Tm, Lu, Y) appear as a new family of kagome metals, structurally
analogous to $R$V$_6$Sn$_6$ ($R$ = Sc, Y, or rare earth) systems. Among them,
LuNb$_6$Sn$_6$ emerges as a novel material hosting charge density wave (CDW)
with a $sqrt{3}$ $times$ $sqrt{3}$ $times$ $3$ wave vector, akin to that in
ScV$_6$Sn$_6$. Here, we employ high-resolution angle-resolved photoemission
spectroscopy, scanning tunneling microscopy, and density functional theory
calculations to systematically investigate the electronic properties of
LuNb$_6$Sn$_6$. Our observation reveals the characteristic band structures of
the "166" kagome system. A charge instability driven by Fermi surface nesting
is decisively ruled out through an analysis of the interactions between van
Hove singularities. Across the CDW transition, we observe orbital-selective
band modifications, with noticeable evolutions of Lu 5$d$ and Sn 5$p$
electrons, while Nb 4$d$ electrons exhibit minimal change, suggesting that the
Lu and Sn sites other than the Nb kagome lattice play a key role in the
formation of CDW. Our findings substantiate a universal lattice-driven CDW
mechanism rather than a charge-instability-driven one in the "166" kagome
compounds, making it a distinct material class compared to other charge-ordered
kagome systems, such as $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) and FeGe.
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