Very large anisotropy in the dc conductivity of epitaxial VO2 thin films grown on (011) rutile TiO2 substrates

In this letter, we reported a very large anisotropy in dc conductivity of epitaxial VO2 thin films deposited on a (011) TiO2 substrate. The VO2 film grew epitaxially on TiO2 and x-ray diffraction showed that VO2 had the tetragonal symmetry due to the substrate clamping effect at room temperature. There was a compressive strain of -1.2% along the c-axis of the rutile VO2. We observed a very strong angular dependence of in-plane dc conductivity. We calculated that sigma(1)/sigma(3)similar to 5.14, which was anomalously large. We attributed the drastic increase to the compressive strain along the c-axis of the rutile VO2 due to substrate clamping. This very large anisotropy disappeared above the metal-insulator transition.