Photoresponse of a strongly correlated material determined by scanning photocurrent microscopy

The generation of a current by light is a key process in optoelectronic and photovoltaic devices. In band semiconductors, depletion fields associated with interfaces separate long-lived photo-induced carriers. However, in systems with strong electron-electron and electron-phonon correlations it is unclear what physics will dominate the photoresponse. Here, we investigate photocurrent in VO(2), an exemplary strongly correlated material known for its dramatic metal-insulator transition at T(c) ≈ 68 °C, which could be useful for optoelectronic detection and switching up to ultraviolet wavelengths. Using scanning photocurrent microscopy on individual suspended VO(2) nanobeams we observe a photoresponse peaked at the metal-insulator boundary but extending throughout both insulating and metallic phases. We determine that the response is photothermal, implying efficient carrier relaxation to a local equilibrium in a manner consistent with strong correlations. Temperature-dependent measurements reveal subtle phase changes within the insulating state. We further demonstrate switching of the photocurrent by optical control of the metal-insulator boundary arrangement. Our work shows the value of applying scanning photocurrent microscopy to nanoscale crystals in the investigation of strongly correlated materials, and the results are relevant for designing and controlling optoelectronic devices employing such materials.