R. J. Watts-Tobin

Nonequilibrium theory of dirty, current-carrying superconductors: phase-slip oscillators in narrow filaments near T c

General equations for the dynamic behavior of dirty superconductors in the Ginzburg-Landau regime Tc-T ≪ Tcare derived from microscopic theory. In the immediate vicinity of Tca local equilibrium approximation leads to a simple generalized time-dependent Ginzburg-Landau equation. The oscillatory phase-slip solutions presented previously are discussed in greater detail.

A microscopic calculation of the force on a wire moving through superfluid3He-B in the ballistic regime

When a macroscopic object moves through superfluid3He, it experiences a force arising from the effect of quasiparticle scattering. We develop a three-dimensional microscopic model to calculate the force on a smooth cylinder moving at constant velocityv as a model of a vibrating wire. At large (subcritical) wire velocity, the force tends to an asymptotic value as 1/v2, rather than exponentially as in a one-dimensional calculation. At lowv the force is linear inv. We briefly discuss the agreement of our calculations with experimental measurements on a vibrating wire below 0.2Tc, where the quasiparticle trajectories are ballistic.

Diffuse scattering model of the thermal damping of a wire moving through superfluid3He-B at very low temperatures

We present a microscopic model of the scattering of quasiparticles in superfluid3He-B by a moving solid surface. This is used to calculate the thermal damping of a wire resonator in the low temperature regime. The calculated damping force is in good agreement with experimental results when the quasiparticles are assumed to be scattered diffusely by the wire.

Microscopic theory of the current-voltage relationship across a normal-superconducting interface

Measurements by Pippardet al. have shown the existence of an extra resistance due to the penetration of an electrical potential into a superconductor. Previous theories of this effect are unable to explain the full temperature dependence of the extra resistance because they use oversimplified models of the normal superconducting interface. We show that the microscopic theory for dirty superconductors leads to a good agreement with experiment over the whole temperature range.

Transport coefficients in the mixed state of dirty superconductors

We present a general formalism for the calculation of electronic transport properties in inhomogeneous superconducting alloys, neglecting fluctuations of the self-consistent potentials. All previously known results can easily be rederived as limiting cases and for the first time the ultrasonic absorption and thermal conductivity are determined numerically throughout the whole mixed state regime.

Transverse thermal conductivity of a dirty superconductor in the mixed state

We consider a dirty superconductor in the mixed state with a temperature gradient applied transverse to the magnetic flux. Using microscopic time-dependent superconductivity theory, we obtain formulas for the thermal conductivity of the electrons. The results agree with earlier phenomenological calculations at low temperature. At higher temperatures the theories do not coincide.

Specular and diffuse scattering of quasiparticles by a macroscopic object moving through superfluid3He-B

When a wire resonator is moving in superfluid3He-B at low temperature, there is a drag force due to scattering of thermally excited quasiparticles. The form of the graph of the drag force against the wire velocity depends strongly on the type of scattering at the wire surface. The force always rises linearly at zero velocity, and it tends to a limiting value at high wire velocity. However the graph is much more sharply curved if the scattering is diffuse than if it is specular. Here we present an analytic study of the form of the graph, by making estimates of the effect of Andreev reflection of scattered quasiparticles in the superflow round the wire. We show that the differences between diffuse and specular scattering can be understood intuitively, by considering the geometrical restrictions imposed by Andreev reflection on the scattering at the wire surface.

Ultrasonic attenuation in the mixed state of a dirty superconductor

Transport coefficients in the mixed state have simple expressions when the response is local. For dirty materials the ultrasonic attenuation is given by the local expression over the whole mixed-state regime because of the Coulomb interaction between the electrons, and responses of the order parameter and magnetic field to the sound wave do not contribute to the attenuation. Computations based on the theory are compared with experiment.

Anisotropy of the thermal conductivity of a dirty superconductor in the mixed state

We present numerical calculations of the anisotropy in the electronic thermal conductivity in the mixed state, and compare the calculations with experiment by estimating the conductivity due to phonons.

Density of states in dirty type II superconductors near Tc

Abstract We have determined the behavior of the density of states in the mixed state of superconducting alloys for T → Tc. The local density of states tends towards the BCS expression with the order parameter playing the role of the energy gap. The singularities are smeared out by the spatial average. The effective normal core radius of a vortex diverges like (1 − T T c ) − 1 3 for T → Tc unlike the coherence length which diverges like (1 − T T c ) − 1 2 .