Spectral properties of the Holstein double-exchange model and application to manganites

TL;DR

This paper investigates the spectral and magnetic properties of the Holstein double-exchange model, applying it to manganites, and finds good agreement with experimental data, highlighting the role of pseudogaps and electron-phonon interactions.

Contribution

It introduces a comprehensive analysis of the Holstein double-exchange model using the many-body coherent potential approximation, connecting theoretical predictions with experimental observations in manganites.

Findings

Pseudogap at Fermi level influences spectral properties.

Spin-wave stiffness decreases with electron-phonon coupling g.

Agreement with ARPES and optical measurements in manganites.

Abstract

Calculations of one-electron spectral functions, optical conductivity and spin-wave energy in the Holstein double-exchange model are made using the many-body coherent potential approximation. Satisfactory agreement is obtained with angle-resolved photoemission results on La_1.2Sr_1.8Mn_2O_7 and optical measurements on Nd_0.7Sr_0.3MnO_3. A pseudogap in the one-electron spectrum at the Fermi level plays an important role in both systems, but a small-polaron band is only predicted to exist in the La system. A rigorous upper bound on spin-wave energies at T=0 is derived. The spin-wave stiffness constant D decreases with increasing electron-phonon coupling g in a similar way to the Curie temperature Tc, but D/(k_B Tc) increases for large g (low Tc) as observed experimentally.