Anomalous bond stretching phonons as a probe of charge fluctuations in perovskites

TL;DR

This paper presents a model linking anomalous bond stretching phonons to charge fluctuations in perovskites, enabling the extraction of charge response information from phonon measurements.

Contribution

It introduces a semiphenomenological model connecting phonon anomalies to charge modes, aiding interpretation of experimental data in cuprates and perovskites.

Findings

Phonon dispersion and linewidth reveal charge excitation energies.

Model provides a framework for interpreting inelastic scattering experiments.

Proposes isotope substitution experiments for detailed charge mode analysis.

Abstract

Important information on momentum resolved low energy charge response can be extracted from anomalous properties of bond stretching in plane phonons observed in inelastic neutron and X-ray scattering in cuprates and some other perovskites. We discuss a semiphenomenological model based on coupling of phonons to a single charge mode. The phonon dispersion and linewidth allow to locate the energy of the charge excitation in the mid infrared part of the spectrum and to determine some of its characteristics. New experiments on oxygen isotope substitution could allow to achieve a more detailed description. Corresponding relations following from the model can be used for the interpretation of experiments and as test of the model.