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Metal-Insulator Phase Transition in VO2: A Look from the Far Infrared Side

Published online by Cambridge University Press:  01 February 2011

Peter Uhd Jepsen ,
Bernd M. Fischer ,
Andreas Thoman ,
Hanspeter Helm ,
J. Y. Suh ,
Rene Lopez  and
Richard F. Hanglund Jr.
Peter Uhd Jepsen
Affiliation:
jepsen@com.dtu.dk, Technical University of Denmark, COM-DTU - Department of Communications, Optics & Materials, Ørsteds Plads, Building 345V, Kongens Lyngby, N/A, DK-2800, Denmark
Bernd M. Fischer
Affiliation:
bfischer@eleceng.adelaide.edu.au, University of Adelaide, Electrical Engineering, Adelaide, N/A, N/A, Australia
Andreas Thoman
Affiliation:
andreas.thoman@physik.uni-freiburg.de, University of Freiburg, Department of Molecular and Optical Physics, Freiburg, N/A, D-79104, Germany
Hanspeter Helm
Affiliation:
hanspeter.helm@physik.uni-freiburg.de, University of Freiburg, Department of Molecular and Optical Physics, Freiburg, N/A, D-79104, Germany
J. Y. Suh
Affiliation:
j.y.suh@vanderbilt.edu, Vanderbilt University, Department of Physics, Nashville, TN 37235, United States
Rene Lopez
Affiliation:
rene.lopez@vanderbilt.edu, Vanderbilt University, Department of Physics, Nashville, TN 37235, United States
Richard F. Hanglund Jr.
Affiliation:
richard.haglund@vanderbilt.edu, Vanderbilt University, Department of Physics, Nashville, TN 37235, United States
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Abstract

Vanadium dioxide (VO2) displays a well-known metal-insulator (MI) transition at a temperature of 68°C. In this study we use terahertz time-domain spectroscopy (THz-TDS) to investigate the optical properties of VO2 thin films in the vicinity of the MI transition temperature in the frequency range 0.1 – 1.5 THz. We observe the interesting effect that the phase of the transmitted THz field through the conducting VO2 film is delayed in comparison to the phase of the same THz signal transmitted through the insulating VO2 film. This is in contrast to the expected behavior of a homogeneous, conducting film. This observation shows that even at temperatures significantly above the transition temperature, the formation of a homogeneous, conducting film is incomplete. We demonstrate that effective-medium theory (EMT) in combination with a Drude model accounting for the conductivity of metallic domains formed in the VO2 film accounts for all our observations. We show that the Maxwell-Garnett EMT is consistent with our observations, whereas the Bruggeman EMT fails to account for our observations.

Keywords

phase transformationinfrared (IR) spectroscopydielectric properties
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 935: Symposium K – Materials Research for THz Applications , 2006 , 0935-K01-09
Copyright
Copyright © Materials Research Society 2006

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