Photocurrent in Vanadium Dioxide

We investigate the photoresponse of VO$_{2}$~using scanning photocurrent microscopy below and above the metal-insulator transition at 67 \r{ }C. To avoid complications of nonuniform strain and twinning boundaries we focus on single-crystal suspended nanobeams, where the strain is either minimal or well controlled. At intermediate temperatures the metallic and insulating phases coexist and a photocurrent and photoconductance associated with the boundary between them is seen. The magnitude and profile of the photoresponse above and below the transition demonstrates a photothermal mechanism, with fast electron-lattice relaxation and absence of built-in electric fields in the insulating phase consistent with strong electron-electron correlations and a short screening length.