Subdominant $d$-wave interaction in superconducting CaKFe${}_4$As${}_2$?

Abstract

We report inelastic light scattering results on the stoichiometric and fully ordered superconductor CaKFe${}_4$As${}_2$ as a function of temperature and light polarization. In the energy range between 10 and 315 cm${}^{-1}$ (1.24 and 39.1 meV) we observe the particle-hole continuum above and below the superconducting transition temperature $T_c$ and 7 of the 8 Raman active phonons. The main focus is placed on the analysis of the electronic excitations. Below $T_c$ all three symmetries projected with in-plane polarizations display a redistribution of spectral weight characteristic for superconductivity. The energies of the pair-breaking peaks in $A_{1g}$ and $B_{2g}$ symmetry are in approximate agreement with the results from photoemission studies. In $B_{1g}$ symmetry the difference between normal and superconducting state is most pronounced, and the feature is shifted downwards with respect to those in $A_{1g}$ and $B_{2g}$ symmetry. The maximum peaking at 134 cm${}^{-1}$ (16.6 meV) has a substructure on the high-energy side. We interpret the peak at 134 cm${}^{-1}$ in terms of a collective Bardasis-Schrieffer (BS) mode and the substructure as a remainder of the pair-breaking feature on the electron bands. There is a very weak peak at 50 cm${}^{-1}$ (6.2 meV) which is tentatively assigned to another BS mode.

arXiv comment8 pages, 9 figures

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• Raman Study of Cooper Pairing Instabilities in (Li${}_{1-x}$Fe${}_x$)OHFeSe
• Linear optical response from the odd parity Bardasis-Schrieffer mode in locally non-centrosymmetric superconductors
• Evidence of a distinct collective mode in Kagome superconductors
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• Electronic signatures of successive itinerant, magnetic transitions in hexagonal La2Ni7
• The role of orbital nesting in the superconductivity of Iron-based Superconductors
• Anisotropic superconductivity and Fermi surface reconstruction in the spin-vortex antiferromagnetic superconductor CaK(Fe${}_{0.95}$Ni${}_{0.05}$)${}_4$As${}_4$
• Higgs mode stabilization by photo-induced long-range interactions in a superconductor
• Signatures of Bardasis-Schrieffer mode excitation in Third-Harmonic generated currents
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