An unconventional platform for kagome flat bands on semiconductor surfaces

Jae Hyuck Lee

Finding new kagome systems for flat band physics has been a recent hot topic in condensed matter physics. Here we propose a new platform for kagome flat bands on semiconductor surfaces. We study a new type of kagome system existent in a metal - semiconductor surface state; one monolayer Ag/Si(111) √3×√3. The silver atoms form a distorted breathing kagome lattice on the silicon. 

 By ARPES measurement, we find that there exists a flat band below the Fermi level across most of the Brillouin zone and a quadratic band touching at the Γ point. Through density functional theory and tight-binding calculations, we elucidate that this flat band is indeed a novel d-orbital hybridized kagome flat band, which is created by destructive interference resulting from a careful balance between the hopping parameters of the in-plane d-orbitals of the silver atoms. 

Such observation of kagome flat bands in materials hosting distorted kagome lattice is uncommon, though certainly not unheard of, since the likes of the breathing distortion usually deter a complete destructive interference. Moreover, such surface based system has not been a conventional approach to the realization of kagome lattices and kagome bands. This work opens up a new avenue in exploring flat bands and designing ideal two-dimensional kagome systems.