Optical Response of High-Dielectric-Constant Perovskite-Related Oxide
C. C. Homes,1*
T. Vogt,1
S. M. Shapiro,1
S. Wakimoto,12
A. P. Ramirez3
Optical conductivity measurements on the perovskite-related
oxide CaCu3Ti4O12 provide a
hint of the physics underlying the observed giant dielectric effect in
this material. A low-frequency vibration displays anomalous behavior,
implying that there is a redistribution of charge within the unit cell
at low temperature. At infrared frequencies (terahertz), the value for
the dielectric constant is ~80 at room temperature, which is far
smaller than the value of ~105 obtained at lower radio
frequencies (kilohertz). This discrepancy implies the presence of a
strong absorption at very low frequencies due to dipole relaxation. At
room temperature, the characteristic relaxation times are fast (
500
nanoseconds) but increase dramatically at low temperature, suggesting
that the large change in dielectric constant may be due to a
relaxor-like dynamical slowing down of dipolar fluctuations in nanosize
domains.
1 Department of Physics, Building 510B,
Brookhaven National Laboratory, Upton, NY 11973-5000, USA.
2 Department of Physics, Massachusetts Institute of
Technology, Cambridge, MA 02139-4307, USA.
3 Condensed Matter and Thermal Physics Group, MST-10
K764, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
*
To whom correspondence should be addressed. E-mail:
homes{at}bnl.gov
Present address: Department of Physics, University of
Toronto, 60 St. George Street, Toronto, Ontario, Canada, M5S 1A7.
