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Content:
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Abstract:
One common attribute of several classes of correlated electron systems is that the insulator-tometal
transition in these systems typically occurs in the regime of nano-scale phase separation of
chemical, and/or electronic/magnetic origin [1]. These intrinsic non-uniformities complicate the
inquiry into the roles of lattice/structural transformations and many body physics in the
emergence of metallicity. Despite rapid progress with the development of scanning probe
techniques, it remains a challenging task to simultaneously probe nano-scale variations of
electronic and structural properties over macroscopic regions [2]. We have accomplished this
task using advanced nano-infrared methods that we have applied to investigate crystalline films
of a prototypical correlated oxide VO2. Recent experiments [3] have allowed us to visualize the
route cause of the electronic anisotropy and memory effects [4] in this material. Through nanospectroscopic
monitoring of the lattice and free carrier dynamics in VO2 we uncovered three
different stages of the insulator-to-metal transition characterized by distinct electron-lattice
effects.
[1] D. N. Basov, Richard D. Averitt, Dirk van der Marel, Martin Dressel, and Kristjan Haule
“Electrodynamics of correlated electron materials” Reviews of Modern Physics 83, 471 (2011)
[2] Dawn A. Bonnell, D. N. Basov, Matthias Bode, Ulrike Diebold, Sergei V. Kalinin, Vidya
Madhavan, Lukas Novotny, Miquel Salmeron, Udo D. Schwarz, and Paul S. Weiss “Imaging
physical phenomena with local probes: From electrons to photons” Reviews of Modern Physics
84, 1343 (2012).
[3] Mengkun Liu, Martin Wagner, Elsa Abreu, Salinporn Kittiwatanakul, Alexander McLeod,
Zhe Fei, Michael Goldflam, Siyuan Dai, Michael Fogler, Jiwei Lu, Stuart A. Wolf, Richard D.
Averitt, D. N. Basov, “Anisotropic electronic state via spontaneous phase separation in strained
Vanadium Dioxide films” (under review).
[4] T.Driscoll, H.T. Kim, B.G. Chae, B.J. Kim, N. Marie Jokerst, S. Palit, D.R. Smith, M. Di
Ventra, D.N. Basov “Memory Metamaterials” Science 325, 1518 (2009).
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