Visualizing the localized electrons of a kagome flat band

Abstract

Destructive interference between electron wavefunctions on the two-dimensional kagome lattice induces an electronic flat band, which could host a variety of interesting quantum states. Key to realize these proposals is to demonstrate the real-space localization of kagome flat-band electrons. The extent to which the complex structure of realistic materials counteract the localizing effect of destructive interference is hitherto unknown. Moreover, a detailed understanding of the real-space distribution of the electronic states of kagome flat bands has not been developed yet. We used scanning tunneling microscopy to visualize the kagome flat band at the surface of CoSn, a kagome metal. Consistent with results from model calculations, we find that the local density of states associated with the kagome flat bands exhibits a unique real-space distribution by which it can be distinguished from the local density of states of dispersive electron bands and trivially localized states, such as well-localized orbitals and surface resonances. Our results further show that these states exhibit an extremely small localization length of two to three angstroms concomitant with a strongly renormalized quasiparticle velocity v≈1×10^{4}m/s, comparable to that of moiré superlattices. Our findings provide fundamental insight into the electronic properties of kagome metals and present a key step for future research on emergent many-body states in these systems.