Orbital polarons versus itinerantegelectrons in doped manganites

2004/11/23 by Maria Daghofer, M. Daghofer, Andrzej M. Oleś +3
Materials Science · Physics and Astronomy · #Advanced Condensed Matter Physics #Magnetic and transport properties of perovskites and related materials #Physics of Superconductivity and Magnetism #cond-mat.str-el

paper · pdf · doi:10.1103/physrevb.70.184430

published as Phys. Rev. B 70, 184430 (2004) · 19 pages, 20 figures

openalex publication_date 2004/11/23 · arxiv created 2005/01/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28

Abstract

We study an effective one-dimensional (1-D) orbital t\text\ensuremath-J model derived for strongly correlated e_g electrons in doped manganites. The ferromagnetic spin order at half filling is supported by orbital superexchange \ensuremath∝J which stabilizes orbital order with alternating x²\ensuremath-y² and 3z²\ensuremath-r² orbitals. In a doped system it competes with the kinetic energy \ensuremath∝t. When a single hole is doped to a half-filled chain, its motion is hindered and a localized orbital polaron is formed. An increasing doping generates either separated polarons or phase separation into hole-rich and hole-poor regions, and eventually polarizes the orbitals and gives a metallic phase with occupied 3z²\ensuremath-r² orbitals. This crossover, investigated by exact diagonalization at zero temperature, is demonstrated both by the behavior of correlation functions and by spectral properties, showing that the orbital chain with Ising superexchange is more classical and thus radically different from the 1-D spin t\text\ensuremath-J model. At finite temperature we derive and investigate an effective 1-D orbital model using a combination of exact diagonalization with classical Monte Carlo for spin correlations. A competition between the antiferromagnetic and ferromagnetic spin order was established at half filling, and localized polarons were found for antiferromagnetic interactions at low hole doping. Finally, we clarify that the Jahn-Teller alternating potential stabilizes the orbital order with staggered orbitals, inducing the ferromagnetic spin order, and enhancing the localized features in the excitation spectra. Implications of these findings for colossal magnetoresistance manganites are discussed.

Citations

• Uniform hopping approach to the ferromagnetic Kondo model at finite temperature
• Low-temperature Lanczos method for strongly correlated systems
• Spectral Weight of the Hubbard Model through Cluster Perturbation Theory
• Effective spinless fermions in the strong-coupling Kondo model
• Systematic numerical study of spin-charge separation in one dimension
• Evolution of the Low-Frequency Spin Dynamics in Ferromagnetic Manganites
• Orbital polarons in the metal-insulator transition of manganites