Collective modes and sound propagation in a p-wave superconductor: Sr_ {2} RuO_ {4}

Physical Review B (Impact Factor: 3.74). 08/2000; 62:5877. DOI: 10.1103/PhysRevB.62.5877
Source: arXiv


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.

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    ABSTRACT: We have analyzed heat capacity and thermal conductivity measurements of Sr2RuO4 in the normal and superconducting state and come to the conclusion that an order parameter with nodal lines on the Fermi surface is required to account for the observed low-temperature behavior. A gapped order parameter is inconsistent with the reported thermodynamic and transport data. Guided by a strongly peaked dynamical susceptibility along the diagonals of the Brillouin zone in neutron scattering data, we suggest a spin-fluctuation mechanism that would favor the pairing state with the gap maxima along the zone diagonals (such as for a d_{xy} gap). The most plausible candidates are an odd parity, spin-triplet, f-wave pairing state, or an even parity, spin-singlet, d-wave state. Based on our analysis of possible pairing functions we propose measurements of the ultrasound attenuation and thermal conductivity in the magnetic field to further constrain the list of possible pairing states.
    Full-text · Article · May 2000 · Physical Review B
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    ABSTRACT: We have calculated all order-parameter collective modes and their contributions to the spin and charge susceptibilities for possible p-wave pairing states in Sr2RuO4. The susceptibilities are calculated for pairing states having gaps without and with nodes, and for wave vectors q=0 and nesting vector q=Q associated with the α and β bands of Sr2RuO4. Important for the observability of the spin-fluctuation modes, for example, by spin resonance or neutron scattering, and of the charge-fluctuation modes by ultrasound, is the effect of quasiparticle damping. This effect is taken into account and discussed in connection with recent neutron-scattering data on Sr2RuO4.
    No preview · Article · Aug 2000 · Physical Review B
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    ABSTRACT: Effects of order parameter collective modes on electromagnetic response are studied for a clean spin-triplet superconductor with kx+/-iky orbital symmetry, which has been proposed as a candidate pairing symmetry for Sr2RuO4. It is shown that the kx+/-iky superconductor has characteristic massive collective modes analogous to the clapping mode in the A phase of superfluid 3He. We discuss the contribution from the collective modes to ultrasound attenuation and electromagnetic absorption. We show that in the electromagnetic absorption spectrum the clapping mode gives rise to a resonance peak well below the pair breaking frequency, while the ultrasound attenuation is hardly influenced by the collective excitations.
    Full-text · Article · Aug 2000 · Physical Review B
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