Linear optical response from the odd parity Bardasis-Schrieffer mode in locally non-centrosymmetric superconductors

Abstract

On the recent report of a magnetic field induced first order transition between an even-parity superconductivity and an odd-parity superconductivity in $\mathrm{CeR}{\mathrm{h}}_2\mathrm{A}{\mathrm{s}}_2$, the microscopic physics is still under investigation. However, if, in the vicinity of this transition, the coupling strengths of the even and odd pairing channels are comparable, a particle-particle excitonic collective mode referred to as the Bardasis-Schrieffer (BS) mode should generically exist below the pair-breaking continuum. This BS mode can couple to the light and thus affect the optical response of the superconductor, as it arises from a pairing channel with the parity opposite to that of the ground state pairs. Here, by using a generic bilayer model Hamiltonian for the electronic degree of freedom, which is globally centrosymmetric despite each layer being locally non-centrosymmetric, we study the change of the excitation gap of the BS mode with respect to the out-of-plane magnetic fields and demonstrate that its coupling to the light is possible even in the linear response regime. The linear coupling is attributed to the presence of multiple electronic bands, which is a generic feature of a bilayer system. Our result shows the microwave absorption as the signature of the BS mode, and hence a smoking gun signature of the parity-switching at the transition between two superconducting phases.

arXiv comment17 pages, 7 figures, 1 table

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Cited by in corpus (9)

• Light-induced switching between singlet and triplet superconducting states
• Appearance of $c$-axis magnetic moment in odd-parity antiferromagnetic state in CeRh${}_2$As${}_2$ revealed by ${}^{75}$As-NMR
• Field-induced superconductivity mediated by odd-parity multipole fluctuation
• Bardasis-Schrieffer-like phase mode in a superconducting bilayer
• Superconducting meron phase in locally noncentrosymmetric superconductors
• Reciprocal and nonreciprocal paraconductivity in bilayer multiphase superconductors
• Vertex correction for the linear and nonlinear optical responses in superconductors: multiband effect and topological superconductivity
• Quasiclassical theory of vortex states in locally non-centrosymmetric superconductors: application to CeRh${}_2$As${}_2$
• Raman response of collective modes in multicomponent superconductors