B_1g Raman response near an Ising-nematic quantum critical point: properties of a quasielastic peak

Raman scattering has long been used to probe dynamical electronic correlations in various condensed matter systems. Here we present a theoretical study of the B_1g channel Raman response in the vicinity of an Ising-nematic quantum critical point (QCP) in two space dimensions. We show the appearance of a “quasi-elastic peak” as the QCP is approached. The peak frequency is related to the relaxation rate of the deformation of the Fermi surface in the angular momentum l=2 channel, while the peak intensity is directly proportional to the Ising-nematic thermodynamic susceptibility. We discuss our results in the context of iron selenide materials which host such a quantum critical point.