Effect of charge ordering/ disordering on Raman line shape in manganites

Abstract

Manganites are characterized by a fascinating interplay of double exchange, spin and charge fluctuations, and orbital excitations. In this paper we focus attention on charge fluctuations and concomitant charge ordering/disordering, influenced by phonons. Our theoretical results, based on a resolvent expansion of the time-development operator (propagator), are specially tailored for calculating normal mode correlation functions, relevant for optic modes and the associated Raman scattering. The computed line shape, and the resultant line shift and linewidth, are compared with experiments in Pr_0.63Ca_0.37MnO₃. While the line shift data agree well with theory, the linewidth results indicate that charge (dis)ordering may not be the only relaxation mechanism in this system.