15 research outputs found
Carrier dynamics and infrared-active phonons in c-axis oriented RuSrGdCuO film
The conductivity spectra of c-axis oriented thin RuSrGdCuO film
on SrTiO substrate, prepared by pulsed-laser deposition, are obtained from
the analysis of the reflectivity spectra over broad frequency range and
temperatures between 10 and 300 K. The free charge carriers are found to be
strongly overdamped with their scattering rate (1.0 eV at room temperature)
exceeding the plasma frequency (0.55 eV). Four phonon lines are identified in
the experimental spectra and assigned to the specific oxygen related in-plane
polarized vibrations based on the comparison with the results of a lattice
dynamics shell model calculations.Comment: 3 pages, 4 figure
s and d-wave symmetries of the solutions of the Eliashberg equations
We examine the different possible symmetries of the superconducting gap
obtained by solving the Eliashberg equations. We consider an electron-phonon
interaction in a strong coupling scenario. The Coulomb pseudopotential plays
the crucial role of providing the repulsion needed to favour the d-wave
symmetry. But the key parameter that allows very anisotropic solutions even
with very strong coupling is the small angular range of the interaction due to
predominantly electron-phonon forward scattering that is found in the high-Tc
superconductors. We find both s and d-wave solutions whose stability depends
mainly on the angular range of the interaction.Comment: Uuencoded LaTeX file anf 6 Postscript figures (14 pages). Accepted
for publication in Physica
Conductivity of CuO-Chains: Disorder versus Electron-Phonon Coupling
The optical conductivity of the CuO-chains, a subsystem of the 1-2-3
materials, is dominated by a broad peak in the mid-infrared (eV), and a slowly falling high-frequency tail. The 1D --model is
proposed as the relevant low-energy Hamiltonian describing the intrinsic
electronic structure of the CuO-chains. However, due to charge-spin
decoupling, this model alone cannot reproduce the observed \sw. We consider
two additional scattering mechanisms: (i) Disregarding the not so crucial spin
degrees of freedom, the inclusion of strong potential disorder yields excellent
agreement with experiment, but suffers from the unreasonable value of the
disorder strength necessary for the fit. (ii) Moderately strong polaronic
electron-phonon coupling to the mode involving Cu(1)-O(4) stretching, can be
modeled within a 1D Holstein Hamiltonian of spinless fermions. Using a
variational approximation for the phonon Hilbert space, we diagonalize the
Hamiltonian exactly on finite lattices. As a result of the experimental hole
density , the chains can exhibit strong charge-density-wave (CDW)
correlations, driven by phonon-mediated polaron-polaron interactions. In the
vicinity of half filling, charge motion is identified as arising from moving
domain walls, \ie defects in the CDW. Incorporating the effect of vacancy
disorder by choosing open boundary conditions, good agreement with the
experimental spectra is found. In particular, a high-frequency tail arises as a
consequence of the polaron-polaron interactions.Comment: 42 pages, ETH-TH/93-31 (Postscript