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arXiv · 1907.01548

Influence of scattering on optical response of superconductivity

F. Yang·M. W. Wu
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Abstract

By using the gauge-invariant kinetic equation, we analytically investigate the influence of the scattering on the optical properties of superconductors in the normal-skin-effect region. Both linear and second-order responses are studied under a multi-cycle terahertz pulse. In the linear regime, we reveal that the optical absorption $σ_{1s}(ω)$, which origins from the scattering, exhibits a crossover point at $ω=2|Δ|$. Particularly, it is further shown that when $ω<2|Δ|$, $σ_{1s}(ω)$ from the scattering always exhibits a finite value even at low temperature, in contrast to the vanishing $σ_{1s}(ω)$ in the anomalous-skin-effect region as the Mattis-Bardeen theory revealed. In the second-order regime, responses of the Higgs mode during and after the optical pulse are studied. During the pulse, we show that the scattering causes a phase shift in the second-order response of the Higgs mode. Particularly, this phase shift exhibits a significant $π$-jump at $ω=|Δ|$, which provides a very clear feature for the experimental detection. After the pulse, by studying the damping of the Higgs-mode excitation, we reveal a relaxation mechanism from the elastic scattering, which shows a monotonic enhancement with the increase of the impurity density.

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F. Yang, M. W. Wu. 2019-12-18. Influence of scattering on optical response of superconductivity. https://doi.org/10.1103/physrevb.102.144508

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