7 research outputs found
Light scattering study of low-energy vibrational excitations in the metallic glass NiZr using electronic Raman scattering
The Raman response of the metallic glass NiZr is measured as a
function of polarization and temperature and analyzed theoretically.
Unexpectedly, the intensity in the range up to 300\wn increases upon cooling,
which is counterintuitive when the response originates from vibrations alone as
in insulators. The increase finds a natural explanation if the conduction
electrons are assumed to scatter on localized vibrations with a scattering
probability proportional to the Debye-Waller factor. None of our assumptions is
material specific, and the results are expected to be relevant for disordered
systems in general.Comment: 5 pages, 3 figure
Impurity effects in unconventional density waves in the unitary limit
We investigate the effect of strong, nonmagnetic impurities on
quasi-one-dimensional conventional and unconventional density waves (DW and
UDW). The conventional case remains unaffected similarly to s-wave
superconductors in the presence of weak, nonmagnetic impurities. The
thermodynamic properties of UDW were found to be identical to those of a d-wave
superconductor in the unitary limit. The real and imaginary part of the optical
conductivity is determined for electric fields applied in the perpendicular
directions. A new structure can be present corresponding to excitations from
the bound state at the Fermi energy to the gap maximum in addition to the usual
peak at 2\Delta. In the dc limit, universal electric conductivity is found.Comment: 9 pages, 5 figure
Two-dimensional imaging of the spin-orbit effective magnetic field
We report on spatially resolved measurements of the spin-orbit effective
magnetic field in a GaAs/InGaAs quantum-well. Biased gate electrodes lead to an
electric-field distribution in which the quantum-well electrons move according
to the local orientation and magnitude of the electric field. This motion
induces Rashba and Dresselhaus effective magnetic fields. The projection of the
sum of these fields onto an external magnetic field is monitored locally by
measuring the electron spin-precession frequency using time-resolved Faraday
rotation. A comparison with simulations shows good agreement with the
experimental data.Comment: 6 pages, 4 figure
Carrier relaxation, pseudogap, and superconducting gap in high-Tc cuprates: A Raman scattering study
We describe results of electronic Raman-scattering experiments in differently
doped single crystals of Y-123 and Bi-2212. The comparison of AF insulating and
metallic samples suggests that at least the low-energy part of the spectra
originates predominantly from excitations of free carriers. We therefore
propose an analysis of the data in terms of a memory function approach.
Dynamical scattering rates and mass-enhancement factors for the carriers are
obtained. In B2g symmetry the Raman data compare well to the results obtained
from ordinary and optical transport. For underdoped materials the dc scattering
rates in B1g symmetry become temperature independent and considerably larger
than in B2g symmetry. This increasing anisotropy is accompanied by a loss of
spectral weight in B2g symmetry in the range between the superconducting
transition at Tc and a characteristic temperature T* of order room temperature
which compares well with the pseudogap temperature found in other experiments.
The energy range affected by the pseudogap is doping and temperature
independent. The integrated spectral loss is approximately 25% in underdoped
samples and becomes much weaker towards higher carrier concentration. In
underdoped samples, superconductivity related features in the spectra can be
observed only in B2g symmetry. The peak frequencies scale with Tc. We do not
find a direct relation between the pseudogap and the superconducting gap.Comment: RevTeX, 21 pages, 24 gif figures. For PostScript with embedded eps
figures, see http://www.wmi.badw-muenchen.de/~opel/k2.htm
Plasmonic dynamic screening in a gold film by intense femtosecond laser light
It has been found experimentally that in intense femtosecond laser fields the surface plasmon dispersion has an oscillatory character as a function of the exciting laser intensity. It has been interpreted as the result of the dynamic screening of electrons by the strong laser field. A simple model is described in addition to the experimental results, being in good agreement with these findings. The results imply an electron effective mass of around 10 percent lighter than the free electron mass. The effective mass decreases with increasing laser intensity
Infrared and electronic Raman response of coexisting d-wave density wave and d-wave superconductivity
We present mean-field calculations for the in-plane optical conductivity, the superfluid density, and the electronic
Raman susceptibility in quasi two-dimensional systems possessing a ground state with two competing order parameters: d-wave
density wave (dDW) and d-wave superconductor (dSC). In the coexisting dDW+dSC phase we calculate the frequency dependence of
these correlation functions in the presence of impurity scattering in the unitary limit, relevant to zinc-doped cuprate
superconductors