Immense Fano Resonance Induced by Half van der Waals Metals

Interference between quasiparticles in solid-state materials provides an in-depth understanding of the coupling mechanism, such as electron-phonon or phonon-phonon coupling, and the optical and electronic properties of the material. Fano resonance, an interference effect between a discrete excited state and a continuum of excited states, is characterized by an asymmetric line shape in the scattering spectrum with an asymmetry parameter 1/q. For Fano resonance that involves a Raman-active phonon, the degree of asymmetry is typically small due to the relatively weak interference. In this work, we present Fano resonance in an atomically thin metal intercalated between graphene and SiC, where the degree of asymmetry in Fano resonance is over two orders of magnitude higher than in previous reports. This asymmetry factor can also be controlled by physical parameters including temperature and excitation wavelength, whose mechanism is studied by first-principles calculations. The ability to tune the strength of Fano resonance paves the way toward engineering interference effect between quasiparticles at the nanoscale limit.