Raman scattering as a probe of nematic correlations

TL;DR

This paper investigates how Raman scattering can detect nematic correlations in underdoped iron-based superconductors by analyzing orbital and spin fluctuations within a symmetry-constrained low energy Hamiltonian, revealing a quasi-elastic peak near nematic instability.

Contribution

It introduces a symmetry-based low energy model to connect Raman scattering features with nematic correlations in iron-based superconductors, highlighting the critical slow-down near the nematic transition.

Findings

Raman spectral function shows a quasi-elastic peak near nematic instability.

Coupling between orbital and spin fluctuations occurs only within the same symmetry.

Critical slow-down of nematic correlations causes low-energy Raman scattering enhancement.

Abstract

We use the symmetry constrained low energy effective Hamiltonian of iron based superconductors to study the Raman scattering in the normal state of underdoped iron-based superconductors. The incoming and scattered Raman photons couple directly to orbital fluctuations and indirectly to the spin fluctuations. We computed both couplings within the same low energy model. The symmetry constrained Hamiltonian yields the coupling between the orbital and spin fluctuations of only the same symmetry type. Attraction in B2g symmetry channel was assumed for the system to develop the subleading instability towards the discrete in-plane rotational symmetry breaking, referred to as Ising nematic transition. We find that upon approaching this instability, the Raman spectral function develops a quasi-elastic peak as a function of energy transferred by photons to the crystal. We attribute this low-energy B2g scattering to the critical slow-down associated with the build up of nematic correlations.