Photoresponse of a strongly correlated material determined by scanning photocurrent microscopy

TL;DR

This study uses scanning photocurrent microscopy to explore the photoresponse of vanadium dioxide, revealing a photo-thermal response peaked at the metal-insulator boundary and demonstrating optical control of photocurrent switching.

Contribution

It provides the first detailed investigation of photocurrent in a strongly correlated material using SPCM, highlighting the role of photo-thermal effects and phase boundary control.

Findings

Photoresponse peaks at the metal-insulator boundary.

The response is primarily photo-thermal, indicating efficient carrier relaxation.

Optical control can switch the photocurrent by manipulating phase boundaries.

Abstract

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.