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CAMP Seminar: Hole-lattice Coupling and Photoinduced Insulator-metal Transition in VO2

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CAMP Seminar by Peihong Zhang (University of Buffalo, SUNY)
When
08 October 2013 from 3:30 PM to 4:30 PM
Where
339 Davey Laboratory
Contact Name
Vincent Crespi
Contact Phone
(814) 863-0163
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Vanadium dioxide (VO2) undergoes a metal-insulator transition (MIT) at 340 K. The electronic phase transition is accompanied by a “simultaneous” structural change from a low-temperature monoclinic (M1) to a high-temperature rutile (R) structure. Despite decades of intensive research, the physics behind the MIT remains a subject of unabated debate. Recently, it was found that the phase transition in VO2 can be induced by photo-excitation. Ultrafast spectroscopy also reveals a multi-timescale structural evolution ranging from subpicoseconds to nanoseconds in VO2 upon photo-excitation.

In this talk, I will present a theory that is able to explain the photo-induced insulator-metal transition in VO2 and the related transient and multi-time-scale structural dynamics upon photo-excitation. Holes created by photo-excitation weaken the V-V bonds and eventually break V-V dimers in the M1 phase when the laser fluence reaches a critical value. The breaking of the V-V bonds in turn leads to an immediate electronic phase transition from an insulating to a metallic state while the crystal lattice remains monoclinic in shape. If time permits, I will also discuss a few subtle issues related to the physics of VO2 and challenges to first-principles electronic structure theory.   

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