Anisotropic Electronic State via Spontaneous Phase Separation in Strained Vanadium Dioxide Films
M. K. Liu, M. Wagner, E. Abreu, S. Kittiwatanakul, A. McLeod, Z. Fei, M. Goldflam, S. Dai, M. M. Fogler, J. Lu, S. A. Wolf, R. D. Averitt, and D. N. Basov
Physical Review Letters, 111, p.096602 (2013)
We resolved the enigma of anisotropic electronic transport in strained vanadium dioxide (VO2) films by
inquiring into the role that strain plays in the nanoscale phase separation in the vicinity of the insulator-tometal
transition. The root source of the anisotropy was visualized as the formation of a peculiar
unidirectional stripe state which accompanies the phase transition. Furthermore, nanoscale infrared
spectroscopy unveils distinct facets of electron-lattice interplay at three different stages of the phase
transition. These stages include the initial formation of sparse nonpercolating metallic domains without
noticeable involvement of the lattice followed by an electron-lattice coupled anisotropic stripe state close
to percolation which ultimately evolves into a nearly isotropic rutile metallic phase. Our results provide a
unique mesoscopic perspective for the tunable macroscopic phenomena in strained metal oxide films.