  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 a
vanadium dioxide, an exemplary strongly correlated material known for its
dramatic metal-insulator transition (MIT) at Tc = 68 C which could be useful
for optoelectronic detection and switching up to ultraviolet wavelengths. Using
scanning photocurrent microscopy (SPCM) on individual suspended VO2 nanobeams
we observe photoresponse peaked at the metal-insulator boundary but extended
throughout both insulating and metallic phases. We determine that the response
is photo-thermal, 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 SPCM applied
to nanoscale crystals for investigating strongly correlated materials, and the
results are relevant for designing and controlling optoelectronic devices
employing such materials.
