Magnetic Raman Scattering of Insulating Cuprates

TL;DR

This study investigates magnetic Raman scattering in insulating cuprates using theoretical models to explain spectral features and line shape asymmetries, highlighting the roles of spin interactions and phonons.

Contribution

It introduces a detailed theoretical analysis of Raman profiles in insulating cuprates considering spin and phonon interactions within an extended Hubbard model.

Findings

Spin-phonon interactions influence Raman line shapes.

Cyclic exchange explains linewidth and asymmetry.

Model matches experimental Raman spectra features.

Abstract

We study the $B_{1g}$ and $A_{1g}$ Raman profiles of M$_{2}$Cu$O_{4}$ (with M= La, Pr, Nd, Sm, Gd), Bi$_{2}$Sr$_{2}$Ca$_{0.5}$Y$_{0.5}$Cu$_{2}$O$_{8+y}$%, YBa$_{2}$Cu$_{3}$O$_{6.2}$ and PrBa$_{2}$Cu$_{2.7}$Al$_{0.3}$O$_{7}$ insulating cuprates within the Loudon-Fleury theory, in the framework of an extended Hubbard model for moderate on-site Coulomb interaction $U$. We calculate the non-resonant contribution to these Raman profiles by using exact diagonalization techniques and analyze two types of contributing mechanisms to the line shapes: 4-spin cyclic exchange and spin-phonon interactions. Although these interactions contribute to different parts of the spectra, together, they account for the enhanced linewidth and asymmetry of the $B_{1g}$ mode, as well as the non-negligible intensity of the $A_{1g}$ Raman line observed in these materials.