APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014;
Denver, Colorado
Session Z39: Invited Session: Strongly Correlated Electron Systems, Transition Metal Oxides, Vanadates
11:15 AM–2:15 PM,
Friday, March 7, 2014
Room: Mile High Ballroom 2A-3A
Sponsoring
Unit:
DCMP
Chair: Dimitri Basov, University of California, San Diego
Abstract ID: BAPS.2014.MAR.Z39.3
Abstract: Z39.00003 : Vanadium Dioxide: a reconfigurable disordered metamaterial*
12:27 PM–1:03 PM
Preview Abstract
Abstract
Author:
Federico Capasso
(School of Engineering and Applied Sciences, Harvard University)
In VO$_{2}$ thin films, the Insulator-to-Metal transition occurs
gradually with increasing temperature: Nanoscale inclusions of the metallic
phase emerge in the surrounding insulating-phase VO$_{2}$, which
grow and these metallic inclusions are much smaller than the scale of the
wavelength at infrared frequencies, and thus VO$_{2}$ can be viewed
as a natural, reconfigurable,disordered metamaterial with variable effective
optical properties across the phase transition. connect in a percolation
process, eventually leading to a fully metallic state at the end of the
transition. In Ref. [1], this unique temperature-dependent dispersion of the
effective medium was used to demonstrate that a film of VO$_{2}$,
with thickness ( $\cong $ 150 nm) much smaller than the wavelength,
deposited on sapphire can operate as a temperature tunable absorber; in
particular, nearly perfect absorption was achieved at a particular
temperature for a narrow range of infrared wavelengths. The reflectivity of
such a device varies dramatically and non-monotonically across the phase
transition, with the strong absorption feature appearing during an
intermediate state of VO$_{2}$ as a result of coupling to an
``ultra-thin-film resonance'' [2]. Since the emissivity of an
object is equal to its frequency-dependent absorptivity (Kirchoff's law)
such a thin-film VO$_{2}$-sapphire structure is expected to have an
emissivity that also depends strongly and non-monotonically on temperature.
This structure displays ``perfect'' blackbody-like thermal emissivity over a
narrow wavelength range (approximately 40 cm$^{-1})$, surpassing
the emissivity of our black-soot reference [3]. We observed large
broadband negative differential thermal emittance over a \textgreater 10 C
range: Upon heating, the VO$_{\mathrm{2}}$-sapphire structure emits less
thermal radiation and appears colder on an infrared camera [3].
Our experimental approach allows for a direct measurement and extraction of
the wavelength- and temperature-dependent thermal emittance. Collaborations
with M. A. Kats, S. Ramanathan, D. Sharma, R. Blanchard, P. Genevet, J. Lin,
S. Zhang, C. Ko, Z. Yang, M. M. Qazilbash, D. N. Basov are gratefully
acknowledged.\\[4pt]
[1] M. A. Kats et al. Appl. Phys. Lett. 101,221101 (2012).\\[0pt]
[2] M. A. Kats, R. Blanchard, P. Genevet, and F. Capasso, Nat. Mater. 12, 20 (2012).\\[0pt]
[3] M. A. Kats et al. PRX 3, 041004 (2013).
*Support from AFOSR (Grant No. FA9550-12-1- 0289) is acknowledged
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.MAR.Z39.3