Direct observation of giant metallic domain evolution driven by electric bias in VO2 thin films on TiO2(001) substrate

We report on conductive changes caused by electric bias-driven insulator-to-metal transition in VO2 thin films on a TiO2(001) substrate and observe the evolution of giant metallic domains to reveal their microscopic origin. The metallic domains are anisotropically formed along the direction of applied current or voltage. This anisotropic formation of metallic states causes abrupt increase of conductivity when the fraction rate of metallic states is low, conforming with the directed percolation model. Our results illustrate the importance of spatially localized phase transitions to tune conductive behavior. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772211]