12 research outputs found
Two-fluid description of two-band superconductors
We present a systematic study of the response properties of two-band
(multi-gap) superconductors with spin-singlet (s-wave) pairing correlations,
which are assumed to be caused by both intraband (\lambda_{ii}, i=1,2) and
interband (\lambda_{12}) pairing interactions. In this first of three planned
publications we concentrate on the properties of such superconducting systems
in global and local thermodynamic equilibrium, the latter including weak
perturbations in the stationary long-wavelength limit. The discussion of global
thermodynamic equilibrium must include the solution (analytical in the
Ginzburg-Landau and the low temperature limit) of the coupled self-consistency
equations for the two energy gaps \Delta_i(T), i=1,2. These solutions allow to
study non-universal behavior of the two relevant BCS-M\"uhlschlegel parameters,
namely the specific heat discontinuity \Delta C/C_N and the zero temperature
gaps \Delta_i(0)/\pi k_B T_c, i=1,2. The discussion of a local equilibrium
situation includes the calculation of the supercurrent density as a property of
the condensate, and the calculation of both the specific heat capacity and the
spin susceptibility as properties of the gas of thermal excitations in the
spirit of a microscopic two-fluid description. Non-monotonic behavior in the
temperature dependences of the gaps and all these local response functions is
predicted to occur particularly for very small values of the interband
pair-coupling constant \lambda_{12}.Comment: 22 pages, 8 figure
Electronic Raman response in anisotropic metals
Using a generalized response theory we derive the electronic Raman response
function for metals with anisotropic relaxation rates. The calculations account
for the long--range Coulomb interaction and treat the collision operator within
a charge conserving relaxation time approximation. We extend earlier treatments
to finite wavenumbers () and incorporate inelastic
electron--electron scattering besides elastic impurity scattering. Moreover we
generalize the Lindhard density response function to the Raman case. Numerical
results for the quasiparticle scattering rate and the Raman response function
for cuprate superconductors are presented.Comment: 5 pages, 4figures. accepted in PRB (Brief Report), in pres
Response, relaxation and transport in unconventional superconductors
We investigate the collision-limited electronic Raman response and the
attenuation of ultrasound in spin-singlet d-wave superconductors at low
temperatures. The dominating elastic collisions are treated within a t-matrix
approximation, which combines the description of weak (Born) and strong
(unitary) impurity scattering. In the long wavelength limit a two-fluid
description of both response and transport emerges. Collisions are here seen to
exclusively dominate the relaxational dynamics of the (Bogoliubov)
quasiparticle system and the analysis allows for a clear connection of response
and transport phenomena. When applied to quasi-2-d superconductors like the
cuprates, it turns out that the transport parameter associated with the Raman
scattering intensity for B1g and B2g photon polarization is closely related to
the corresponding components of the shear viscosity tensor, which dominates the
attenuation of ultrasound. At low temperatures we present analytic solutions of
the transport equations, resulting in a non-power-law behavior of the transport
parameters on temperature.Comment: 22 pages, 3 figure