387865 Electron/Hole Injection Drives the Ultrafast Phase Transition of VO2

Tuesday, November 18, 2014: 9:24 AM
International 8 (Marriott Marquis Atlanta)
Bin Wang1,2 and Sokrates Pantelides1,3,4, (1)Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, (2)New address as of Aug. 15, 2014 : School of Chemical, Biological and Materials Engineering, University of Oklahoma, Norman, OK, (3)ORNL, Oak Ridge, TN, (4)Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN

Interplay among the microscopic degrees of freedom in transition-metal oxides can generate macroscopic quantum phenomena that provide functionality in electronic and photonic devices. Here, we report density functional calculations and molecular dynamics simulations of VO2, which undergoes a semiconductor-to-metal phase transition accompanied by a monoclinic-to-rutile structural change at 68 °C.  We find that the lattice vibration at the critical temperature generates a metallic state in the monoclinic structure, which may explain the observed metallic intermediate phase in experiments. Moreover, we find that the electron/hole doping strongly couples with the lattice vibration causing collapse of one particular phonon mode and stimulating the structural phase transition. Molecular dynamics simulations show a temperature-dependence of the required carrier density for the phonon collapse, that is, at higher temperature, fewer free carriers are required. We show that the abrupt change of the vibration results from the weakening of the V-V bonds induced by the hole doping. The tunable phase transition is valuable for various application of VO2, such as memristors and molecular sensors.

Support was provided by the DTRA Grant HDTRA1-10-1-0047, NSF Grant DMR-1207241, and McMinn Endowment at Vanderbilt University. DFT calculations were performed at the DoD AFRL.

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See more of this Session: Synthesis and Applications of Oxide Materials
See more of this Group/Topical: Materials Engineering and Sciences Division