Condensed Matter Physics Seminar
Friday, April 30, 1999, 2 p.m.
Plant Sciences Building, Room 1130
Infrared Hall effect in high-Tc superconductors
(University of Maryland)
Abstract: Since the discovery of cuprate high temperature
superconductors (HTSC) over a decade ago, intense experimental and theoretical
efforts have failed to fully resolve the unconventional behavior of HTSC
in the normal (non-superconducting) state. One of the most puzzling
anomalies in the normal state of HTSC is the temperature dependence of
the DC Hall angle. Furthermore, the scattering rate associated with the
Hall angle shows striking qualitative and quantitative differences from
the rate associated with the longitudinal conductivity. Although
the normal state is a good metal, this behavior has been cited as evidence
for non-Drude and even non-Fermi liquid (FL) physics . A number of
FL models (with low lying electron-like excitations, but an anisotropic
scattering rate [1,2]) and non-FL models (with more exotic excitations
such as spinons and holons ) have been used to explain the DC Hall angle
measurements. By extending Hall angle measurements into the infrared
(IR), we can test the frequency dependence of these models while decreasing
the effects of impurity scattering which can dominate DC measurements.
This is accomplished with a sensitive IR (900-1100 cm-1, 112-136
meV) photolelastic polarization modulation technique which can measure
simultaneously both Faraday rotation and circular dichroism. These two
quantities are used to determine the complex IR Hall angle, which provides
insight into a number of fundamental properties such as scattering rates
and effective masses. Measurements on Au and Cu thin films show anisotropic
scattering rates that are related to the anisotropy of their Fermi surfaces,
in addition to demonstrating the accuracy of this technique. These results
also may be relevant to HTSC where two scattering rates are observed.
Measurements on YBCO thin films are used to test several prevailing theories
on the normal state of HTSC.
 A. T. Zheleznyak et al., Phys. Rev. B 57, 3089 (1998).
 L. B. Ioffe and A. J. Millis, cond-mat/9801092.
 P. W. Anderson, Phys. Rev. Lett. 67, 2092 (1991).
Host: Dennis Drew
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