Electronic confinement and ordering instabilities in colossal magnetoresistive bilayer manganites

TL;DR

This study investigates the electronic structure of bilayer manganites, revealing that charge carriers are confined to single layers, leading to a nested Fermi surface and electronic ordering instabilities influenced by fluctuating electronic and lattice interactions.

Contribution

It provides new insights into the confinement of charge carriers and the nature of electronic ordering instabilities in bilayer manganites, supported by combined experimental and theoretical analysis.

Findings

Bilayer splitting is negligible, indicating charge confinement to single MnO2 layers.

The Fermi surface is strongly nested, affecting electronic properties.

Electronic ordering instabilities are driven by fluctuating electronic and lattice interactions.

Abstract

We present angle-resolved photoemission studies of (La1-zPrz)2-2xSr1+2xMn2O7 with x=0.4 and z=0.1,0.2 and 0.4 along with density functional theory calculations and x-ray scattering data. Our results show that the bilayer splitting in the ferromagnetic metallic phase of these materials is small, if not completely absent. The charge carriers are therefore confined to a single MnO2-layer, which in turn results in a strongly nested Fermi surface. In addition to this, the spectral function also displays clear signatures of an electronic ordering instability well below the Fermi level. The increase of the corresponding interaction strength with z and its magnitude of ~400 meV make the coupling to a bare phonon highly unlikely. Instead we conclude that fluctuating order, involving electronic and lattice degrees of freedom, cause the observed renormalisation of the spectral features.