Raman resonance in iron-based superconductors: The magnetic scenario

Abstract

We perform theoretical analysis of polarization-sensitive Raman spectroscopy on NaFe${}_{1-x}$Co${}_x$As, EuFe$2$As${}_2$, SrFe${}_2$As${}_2$, and Ba(Fe${}_{1-x}$Co${}_x$)${}_2$As${}_2$, focusing on two features seen in the $B_{1g}$ symmetry channel (in one Fe unit cell notation): the strong temperature dependence of the static, uniform Raman response in the normal state and the existence of a collective mode in the superconducting state. We show that both features can be explained by the coupling of fermions to pairs of magnetic fluctuations via the Aslamazov-Larkin process. We first analyze magnetically-mediated Raman intensity at the leading two-loop order and then include interactions between pairs of magnetic fluctuations. We show that the full Raman intensity in the $B_{1g}$ channel can be viewed as the result of the coupling of light to Ising-nematic susceptibility via Aslamazov-Larkin process. We argue that the singular temperature dependence in the normal state is the combination of the temperature dependencies of the Aslamazov-Larkin vertex and of Ising-nematic susceptibility. We discuss two scenarios for the resonance below $T_c$. In one, the resonance is due to the development of a pole in the fully renormalized Ising-nematic susceptibility. The other is the orbital excitonic scenario, in which spin fluctuations generate an attractive interaction between low-energy fermions.

18 pages, 18 figures. Changes from last version: Updated abstract metadata and corrected one typo and one reference

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Cited by in corpus (11)

• Low-energy microscopic models for iron-based superconductors: a review
• Magnetism, superconductivity, and spontaneous orbital order in iron-based superconductors: who comes first and why?
• Nematicity and magnetism in FeSe and other families of Fe-based superconductors
• Competing instabilities, orbital ordering and splitting of band degeneracies from a parquet renormalization group analysis of a 4-pocket model for iron-based superconductors: application to FeSe
• Conservation laws, vertex corrections, and screening in Raman spectroscopy
• Superconductivity and electronic fluctuations in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ studied by Raman scattering
• Raman response in the nematic phase of FeSe
• Quadrupolar charge dynamics in the nonmagnetic FeSe${}_{1-x}$S${}_x$ superconductors
• Theories for charge-driven nematicity in kagome metals
• Superconducting gap and nematic resonance at the quantum critical point observed by Raman scattering in $\mathrm{BaF}{\mathrm{e}}_2({\mathrm{As}}_{1-x}{\mathrm{P}}_x{)}_2$
• Quasiparticle scattering in a superconductor near a nematic critical point: resonance mode and multiple attractive channels