Quantum nonlinear phononics in multilayer graphene accessed by pump-probe Raman scattering

Coherently driven phonons are conventionally treated classically. In the case of nonlinear phonon-phonon interactions, an infrared drive modifies the fluctuation spectrum, causing significant squeezing, making a quantum description essential. We show that nonequilibrium spontaneous Raman scattering is an ideal probe for these quantum properties. We apply this framework to a recent experimental finding suggesting quantum nonlinear phononics in multilayer graphene (E1u and E2g modes). We find that quantum fluctuations contribute to the E2g mode’s spectral modification upon driving the E1u mode. Furthermore, light-mediated interactions cause the optical spring effect observed in the experiment. We argue that quantum fluctuation dynamics need to be considered in experiments invoking nonlinear phononics to induce nonequilibrium phases of matter.

Jakob will be at MPSD on Wednesday. If you would like to meet Jakob in person during the visit, please let Michael Fechner know.