Isotope effect and bond-stretching phonon anomaly in high-Tc cuprates

TL;DR

This paper investigates how bond-stretching phonon anomalies in high-Tc cuprates relate to electron response, proposing a method to reconstruct the electron spectrum from isotope effect measurements, revealing insights into electron-phonon interactions.

Contribution

It introduces a model linking phonon anomalies to electron response and demonstrates how isotope effects can reveal the electron spectrum in high-Tc cuprates.

Findings

Phonon anomalies are caused by coupling to a damped electron oscillator.

Isotope effects can help reconstruct the electron spectrum in the mid-infrared region.

Phonon linewidth is a sensitive probe of isotope effects in incoherent electron regimes.

Abstract

We analyse a model where the anomalies of the bond-stretching LO phonon mode are caused by the coupling to electron dynamic response in the form of a damped oscillator and explore the possibility to reconstruct the spectrum of the latter from the phonon measurements. Preliminary estimates point to its location in the mid infrared region and we show how the required additional information can be extracted from the oxygen isotope effect on the phonon spectrum. The model predicts a significant measurable deviation from the "standard value" of the isotope effect even if the phonon frequency is far below the electron spectrum, provided the latter is strongly incoherent. In this regime, which corresponds to the "mid infrared scenario", the phonon linewidth becomes a sensitive and informative probe of the isotope effect.