Mott Transition in VO2 Revealed by Infrared Spectroscopy and Nano-Imaging
M. M. Qazilbash,1*
M. Brehm,2
Byung-Gyu Chae,3
P.-C. Ho,1
G. O. Andreev,1
Bong-Jun Kim,3
Sun Jin Yun,3
A. V. Balatsky,4
M. B. Maple,1
F. Keilmann,2
Hyun-Tak Kim,3
D. N. Basov1
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.
1 Physics Department, University of California–San Diego, La Jolla, CA 92093, USA.
2 Abt. Molekulare Strukturbiologie, Max-Planck-Institut für Biochemie and Center for NanoScience, 82152 Martinsried, München, Germany.
3 IT Convergence and Components Laboratory, Electronics and Telecommunications Research Institute, Daejeon 305-350, Korea.
4 Theoretical Division and Center for Integrated Nanotechnologies, MS B262, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
* To whom correspondence should be addressed. E-mail: mumtaz{at}physics.ucsd.edu
