Phonon `notches' in a-b -plane optical conductivity of high-Tc superconductors

TL;DR

This paper explains the origin of 'notch'-like features in the in-plane optical conductivity of high-Tc superconductors as resulting from phonon-mediated electron interactions between layers, with the notch size depending on phonon properties.

Contribution

It demonstrates a correlation between phonon modes and conductivity features, highlighting how phonon sharpness and coupling influence the optical conductivity notches in high-Tc superconductors.

Findings

Notches are linked to c-axis LO phonons and interlayer electron interactions.

The size of the notches depends on phonon coupling strength, frequency, and width.

Even weak phonon coupling can produce significant effects if the phonon is sharp.

Abstract

It is shown that a correlation between the positions of the $c$-axis longitudinal optic ($LO_c$) phonons and ``notch''-like structures in the $a$-$b$ plane conductivity of high-$T_c$ superconductors results from phonon-mediated interaction between electrons in different layers. It is found that the relative size of the notches depends on $\lambda_{ph}(\Omega_{ph}/\gamma_{ph})$, where $\lambda_{ph}$, $\Omega_{ph}$ and $\gamma_{ph}$ are the effective coupling strength, the frequency and the width of the optical phonon which is responsible for the notch. Even for $\lambda_{ph}\approx 0.01$ the effect can be large if the phonon is very sharp.