Theory for charge and orbital density-wave states in manganite La$_{0.5}$Sr$_{1.5}$MnO$_4$

TL;DR

This paper presents a theoretical analysis of the charge and orbital density-wave states in layered manganite La$_{0.5}$Sr$_{1.5}$MnO$_4$, explaining the phase transition through Fermi surface nesting and mean field theory.

Contribution

It introduces a mean field theoretical framework to understand charge and orbital ordering driven by Fermi surface nesting in layered manganites.

Findings

Charge and orbital orderings are explained by density wave instability.

Orbital ordering is induced by Fermi surface nesting with specific orbital characters.

Ordered orbitals are identified as $d_{x^2-y^2} ext{ and } d_{3z^2-r^2}$.

Abstract

We investigate the high temperature phase of layered manganites, and demonstrate that the charge-orbital phase transition without magnetic order in La$_{0.5}$Sr$_{1.5}$MnO$_4$ can be understood in terms of the density wave instability. The orbital ordering is found to be induced by the nesting between segments of Fermi surface with different orbital characters. The simultaneous charge and orbital orderings are elaborated with a mean field theory. The ordered orbitals are shown to be $d_{x^2-y^2} \pm d_{3z^2-r^2}$.