11 research outputs found
Signature of stripe pinning in optical conductivity
The response of charge stripes to an external electric field applied
perpendicular to the stripe direction is studied within a diagrammatic approach
for both weak and strong pinning by random impurities. The sound-like mode of
the stripes described as elastic strings moves to finite frequency due to
impurity pinning. By calculating the optical conductivity we determine this
characteristic energy scale for both a single stripe and an array of
interacting stripes. The results explain the anomalous far-infrared peak
observed recently in optical-conductivity measurements on cuprates.Comment: Revised version, to appear in Phys. Rev.
Temperature dependence of the spectral weight in p- and n-type cuprates: a study of normal state partial gaps and electronic kinetic energy
The optical conductivity of CuO2 (copper-oxygen) planes in p- and n-type
cuprates thin films at various doping levels is deduced from highly accurate
reflectivity data. The temperature dependence of the real part sigma1(omega) of
this optical conductivity and the corresponding spectral weight allow to track
the opening of a partial gap in the normal state of n-type Pr{2-x}Ce(x)CuO4
(PCCO), but not of p-type Bi2Sr2CaCu2O(8+delta} (BSCCO) cuprates. This is a
clear difference between these two families of cuprates, which we briefly
discuss. In BSCCO, the change of the electronic kinetic energy Ekin - deduced
from the spectral weight- at the superconducting transition is found to cross
over from a conventional BCS behavior (increase of Ekin below Tc to an
unconventional behavior (decrease of Ekin below Tc) as the free carrier density
decreases. This behavior appears to be linked to the energy scale over which
spectral weight is lost and goes into the superfluid condensate, hence may be
related to Mott physics
Topological (Sliced) Doping of a 3D Peierls System: Predicted Structure of Doped BaBiO3
At hole concentrations below x=0.4, Ba_(1-x)K_xBiO_3 is non-metallic. At x=0,
pure BaBiO3 is a Peierls insulator. Very dilute holes create bipolaronic point
defects in the Peierls order parameter. Here we find that the Rice-Sneddon
version of Peierls theory predicts that more concentrated holes should form
stacking faults (two-dimensional topological defects, called slices) in the
Peierls order parameter. However, the long-range Coulomb interaction, left out
of the Rice-Sneddon model, destabilizes slices in favor of point bipolarons at
low concentrations, leaving a window near 30% doping where the sliced state is
marginally stable.Comment: 6 pages with 5 embedded postscript figure
Localization by disorder in the infrared conductivity of (Y,Pr)Ba2Cu3O7 films
The ab-plane reflectivity of (Y{1-x}Prx)Ba2Cu3O7 thin films was measured in
the 30-30000 cm-1 range for samples with x = 0 (Tc = 90 K), x = 0.4 (Tc = 35 K)
and x = 0.5 (Tc = 19 K) as a function of temperature in the normal state. The
effective charge density obtained from the integrated spectral weight decreases
with increasing x. The variation is consistent with the higher dc resistivity
for x = 0.4, but is one order of magnitude smaller than what would be expected
for x = 0.5. In the latter sample, the conductivity is dominated at all
temperatures by a large localization peak. Its magnitude increases as the
temperature decreases. We relate this peak to the dc resistivity enhancement. A
simple localization-by-disorder model accounts for the optical conductivity of
the x = 0.5 sample.Comment: 7 pages with (4) figures include
Raman Scattering versus Infrared Conductivity: Evidence for one-dimensional Conduction in La_{2-x}Sr_{x}CuO_{4}
Raman and Infrared (IR) spectra of an underdoped La_{1.90}Sr_{0.10}CuO_{4}
single crystal have been measured as a function of temperature. Both techniques
provide unconventional low-energy spectra. The IR conductivity exhibits
features peaked at finite frequencies which do not have a counterpart in the
Raman response. Below approximately 100 K a transfer of both Raman and IR
spectral weight towards lower energies is found and a new component in the
Raman response builds up being characterized by a very long lifetime of
electrons propagating along the Cu-O bonds.Comment: 4 pages, 3 eps figure
Non-linear infrared properties of InAs/GaAs self-assembled quantum dots
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