  In condensed matter physics, materials with kagome lattice display a range of
exotic quantum states, including charge density wave (CDW), superconductivity
and magnetism. Recently, the intermetallic kagome metal ScV6Sn6 was discovered
to undergo a first-order structural phase transition with the formation of a
root3xroot3x3 CDW at around 92 K. The bulk electronic band properties are
crucial to understanding the origin of the structural phase transition. Here,
we conducted an optical spectroscopy study in combination with band structure
calculations across the structural transition. Our findings showed abrupt
changes in the optical reflectivity/conductivity spectra as a result of the
structural transition, without any observable gap formation behavior. The
optical measurements and band calculations actually reveal a sudden change of
the band structure after transition. It is important to note that this phase
transition is of the first-order type, which distinguishes it from conventional
density-wave type condensations. Our results provide an insight into the origin
of the structural phase transition in this new and unique kagome lattice.
