Collective modes and sound propagation in a p-wave superconductor: Sr2RuO4

Abstract

There are five distinct collective modes in the recently discovered p-wave superconductor Sr2RuO4; phase and amplitude modes of the order parameter, clapping mode (real and imaginary), and spin wave. The first two modes also exist in the ordinary s-wave superconductors, while the clapping mode with the energy 2Δ(T) is unique to Sr2RuO4 and couples to the sound wave. Here we report a theoretical study of the sound propagation in a two-dimensional p-wave superconductor. We identified the clapping mode and study its effects on the longitudinal and transverse sound velocities in the superconducting state. In contrast to the case of 3He, there is no resonance absorption associated with the collective mode, since in metals ω/(vF|q|)≪1, where vF is the Fermi velocity, q is the wave vector, and ω is the frequency of the sound wave. However, the velocity change in the collisionless limit gets modified by the contribution from the coupling to the clapping mode. We compute this contribution and comment on the visibility of the effect. In the diffusive limit, the contribution from the collective mode turns out to be negligible. The behaviors of the sound velocity change and the attenuation coefficient near Tc in the diffusive limit are calculated and compared with the existing experimental data wherever it is possible. We also present the results for the attenuation coefficients in both of the collisionless and diffusive limits at finite temperatures.

Source-reported materials — not catalogue approval

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