Vibrational edge modes in intrinsically inhomogeneous doped transition metal oxides

TL;DR

This paper investigates vibrational edge modes in doped transition metal oxides, revealing interface-localized phonon modes that are insensitive to doping levels but increase with interface density, relevant for phase-separated systems.

Contribution

The study identifies and characterizes low-frequency vibrational edge modes in inhomogeneous doped transition metal oxides using theoretical models, highlighting their doping-insensitive energy and interface-dependent intensity.

Findings

Edge modes are pinned to interfaces between electronic regions.

Their energy remains constant across doping levels.

Mode intensity correlates with interface density.

Abstract

By applying an unrestriced Hartree-Fock approximation and a Random Phase approximation to multiband Peierls-Hubbard Hamiltonians, we determine the phonon mode structure in models of transition metal oxides in the presence of intrinsic nanoscale inhomogeneities induced by hole doping. We identify low frequency $local$ vibrational modes pinned to the interface between regions of distinct electronic structure and separated in frequency from the band of extended phonons. A major characteristic of these ``edge'' modes is that their energy is essentially insensitive to the doping level, while their intensity increases with the density of interfaces (and thus doping level). We argue that the presence of such modes is a typical feature of systems with phase separation, including cuprates, nickelates, manganites, and bismuthates. We specifically address the experimental signatures of these modes in lattice inelastic neutron scattering.