title: Mott transition in VO2 revealed by infrared spectroscopy and nano-imaging.
abstract: Electrons in correlated insulators are prevented from conducting by Coulomb repulsion between them. When an insulator-to-metal transition is induced in a correlated insulator by doping or heating, the resulting conducting state can be radically different from that characterized by free electrons in conventional metals. We report on the electronic properties of a prototypical correlated insulator vanadium dioxide in which the metallic state can be induced by increasing temperature. Scanning near-field infrared microscopy allows us to directly image nanoscale metallic puddles that appear at the onset of the insulator-to-metal transition. In combination with far-field infrared spectroscopy, the data reveal the Mott transition with divergent quasi-particle mass in the metallic puddles. The experimental approach used sets the stage for investigations of charge dynamics on the nanoscale in other inhomogeneous correlated electron systems.
authors: Physics Department, University of California-San Diego, La Jolla, CA 92093, USA. mumtaz@physics.ucsd.edu
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authors: Qazilbash
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authors: Brehm
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authors: Andreev
authors: Bong-Jun
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authors: Kim
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authors: Balatsky
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authors: Keilmann
authors: Hyun-Tak
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