Anomalies of the infrared-active phonons in underdoped YBCO as an evidence for the intra-bilayer Josephson effect

TL;DR

This paper investigates the infrared-active phonon anomalies in underdoped YBCO, attributing them to intra-bilayer Josephson effects that influence local ionic fields during the transition to superconductivity.

Contribution

It provides evidence linking phonon anomalies in underdoped YBCO to intra-bilayer Josephson effects, offering a new understanding of superconducting state changes.

Findings

Phonon peak changes are linked to Josephson effects.

Local field modifications explain phonon anomalies.

Superconducting transition affects phonon spectra significantly.

Abstract

The spectra of the far-infrared c-axis conductivity of underdoped YBCO crystals exhibit dramatic changes of some of the phonon peaks when going from the normal to the superconducting state. We show that the most striking of these anomalies can be naturally explained by changes of the local fields acting on the ions arising from the onset of inter- and intra-bilayer Josephson effects.