Electromagnetic absorption in anisotropic superconductors

P. J. Hirschfeld; P. Wölfle; J. A. Sauls; D. Einzel; W. O. Putikka

doi:10.1103/PhysRevB.40.6695

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Electromagnetic absorption in anisotropic superconductors

P. J. Hirschfeld, P. Wölfle, J. A. Sauls, D. Einzel, W. O. Putikka

DOI 10.1103/PhysRevB.40.6695 · Physical Review B

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Abstract

We calculate the absorptive part of the frequency-dependent conductivity for a large class of anisotropic superconductors. The effect of nonmagnetic impurity scattering is included at the level of a self-consistent t-matrix approximation. It is found that low-frequency absorption (0<Ω<2Δ) takes place for any superconducting state with nodes of the energy gap on the Fermi surface. We demonstrate that the limiting low-frequency dependence of σ(Ω) on impurity concentrations can help to determine the structure of the order parameter in candidate systems such as heavy-electron compounds or high-Tc superconductors. We also discuss how strong scattering, similar to that observed in ordinary superconductors doped with Kondo impurities, may lead to absorption with a threshold of Ω≃Δ rather than 2Δ as in quasiisotropic systems. Finally, we consider the contribution of order-parameter collective modes to the electromagnetic absorption, and show that this absorption may be substantial and depends sensitively on the impurity scattering rate.