Photothermal nanoimaging of dissipative surface polaritons*

Controlling the functionalities of 2D material structures via strong light-matter coupling requires understanding of the dissipation and thermalization dynamics of surface polaritons. However, the intricate details of polaritonic decay processes are rooted in a plethora of physical mechanism spanning widely separated length and time scales, even down to regimes where dissipation is no longer a readily measurable quantity.
Here, we introduce photothermal force microscopy as a nanoimaging modality to visualize energy dissipation via surface plasmon polaritons (SPPs). Studying graphene on silicon dioxide, we perform real-space imaging of SPPs via photothermal force detection (AFM-IR) with contrast interpreted due to thermal substrate expansion induced by the local SPP decay. Complementary to previous studies, reporting the optical characterization of SPPs via IR-sSNOM, we will show that photothermal expansion forces facilitate the direct mechanical detection of the non-radiative SPP decay process. Our observations reveal that dissipative surface polariton modes might enable to control the spatio-temporal dynamics of thermal nanosystems.