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arXiv · 1405.6246

Collective modes in multiband superconductors: Raman scattering in iron selenides

M. Khodas·A. V. Chubukov·G. Blumberg
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Abstract

We study Raman scattering in the superconducting state of alkali-intercalated iron selenide materials AxFe2-ySe2 (A=K,Rb,Cs) in which Fermi surface has only electron pockets. Theory predicts that both s-wave and d-wave pairing channels are attractive in this material, and the gap can have either s-wave or d-wave symmetry, depending on the system parameters. ARPES data favor $s-$wave superconductivity. We present the theory of Raman scattering in AxFe2-ySe2 assuming that the ground state has s-wave symmetry but $d-$ wave is a close second. We argue that Raman profile in d-wave B2g channel displays two collective modes. One is a particle-hole exciton, another is a Bardasis-Schrieffer-type mode associated with superconducting fluctuations in d-wave channel. At a finite damping, the two modes merge into one broad peak. We present Raman data for AxFe2-ySe2 and compare them with theoretical Raman profile.

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M. Khodas, A. V. Chubukov, G. Blumberg. 2014-05-23. Collective modes in multiband superconductors: Raman scattering in iron selenides. https://doi.org/10.1103/physrevb.89.245134

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