Nonequilibrium phonon tuning and mapping in few-layer graphene with infrared nanoscopy

Electron-phonon interactions are fundamentally important physical processes responsible for many key discoveries in condensed matter physics and material sciences. Herein, by exploiting the scattering-type scanning near-field optical microscope (s-SNOM) excited with a femtosecond infrared (IR) laser, we explored strong coupling between IR phonons few-layer graphene (FLG) ultrahot electrons, which heated up intense laser field enhanced s-SNOM tip. More specifically, found that intensity of phonon resonance can be tuned systematically varying power controls electron temperature. Furthermore, high spatial resolution allows us to map local characteristics at sharp boundaries nanostructures. Our findings offer insights into intriguing behind electron-phonon nonequilibrium conditions open pathway manipulating means.