title: The nature of photoinduced phase transition and metastable states in vanadium dioxide.
abstract: Photoinduced threshold switching processes that lead to bistability and the formation of metastable phases in photoinduced phase transition of VO2are elucidated through ultrafast electron diffraction and diffusive scattering techniques with varying excitation wavelengths. We uncover two distinct regimes of the dynamical phase change: a nearly instantaneous crossover into an intermediate state and its decay led by lattice instabilities over 10 ps timescales. The structure of this intermediate state is identified to be monoclinic, but more akin to M2rather than M1based on structure refinements. The extinction of all major monoclinic features within just a few picoseconds at the above-threshold-level (~20%) photoexcitations and the distinct dynamics in diffusive scattering that represents medium-range atomic fluctuations at two photon wavelengths strongly suggest a density-driven and nonthermal pathway for the initial process of the photoinduced phase transition. These results highlight the critical roles of electron correlations and lattice instabilities in driving and controlling phase transformations far from equilibrium.
authors.affiliation: Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: Zhensheng
authors.initials: Z
authors.lastname: Tao
authors.affiliation: Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: Faran
authors.initials: F
authors.lastname: Zhou
authors.affiliation: Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: Tzong-Ru T
authors.initials: TT
authors.lastname: Han
authors.affiliation: Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: David
authors.initials: D
authors.lastname: Torres
authors.affiliation: Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: Tongyu
authors.initials: T
authors.lastname: Wang
authors.affiliation: Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: Nelson
authors.initials: N
authors.lastname: Sepulveda
authors.affiliation: Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: Kiseok
authors.initials: K
authors.lastname: Chang
authors.affiliation: Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: Margaret
authors.initials: M
authors.lastname: Young
authors.affiliation: Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 USA.|Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Lunt
authors.affiliation: Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824 USA.
authors.forename: Chong-Yu
authors.initials: CY
authors.lastname: Ruan