Orbital ordering in manganites in the band approach

TL;DR

This paper investigates orbital ordering in manganites like LaMnO3 using a band approach, revealing a nesting-induced instability leading to an orbital density wave and an insulating state.

Contribution

It demonstrates that realistic magnetic structures induce band nesting, causing an excitonic instability and orbital ordering in manganites from a band perspective.

Findings

Existence of complete nesting between e_g-bands in LaMnO3.

Instability towards an excitonic insulator-like state with a gap opening.

Emergence of orbital density wave matching experimental observations.

Abstract

We consider the orbital ordering in LaMnO3 and similar systems, proceeding from the band picture. We show that for the realistic magnetic structure of A-type there exists a complete nesting betweeen two e_g-bands. As a result there occurs an instability towards an excitonic insulator-like state -- an electron-hole pairing with the wave vector Q=(\pi,\pi), which opens a gap in the spectrum and makes the system insulating. In the resulting state there appeasr an orbital ordering -- orbital density wave (ODW), the type of which coincides with those existing in LaMnO3.