Some Considerations on the Additional Absorption Peak in the c-axis Conductivity of Bilayer Cuprate Superconductors: Interpretation of the Changes Induced by a Parallel Magnetic Field and the Role of Bilayer Splitting

TL;DR

This paper investigates the 400 cm^{-1} peak in the c-axis conductivity of bilayer cuprate superconductors, analyzing how a parallel magnetic field affects it and exploring the role of bilayer splitting in the spectral features.

Contribution

It provides a theoretical model linking the peak to the superfluid and calculates the c-axis response considering bilayer splitting, explaining the emergence of additional modes.

Findings

The 400 cm^{-1} peak is consistent with superfluid response.

Moderate bilayer splitting leads to an additional condensate-related mode.

The model aligns with experimental observations of magnetic field effects.

Abstract

Changes of the 400 cm^{-1} peak in the c-axis conductivity of underdoped YBa2Cu3O6.6 upon application of a parallel magnetic field reported by Kojima et al. are shown to be consistent with the model where the peak is due to the superfluid. Results of our calculations of the c-axis response of bilayer compounds with well defined bilayer-split bands are presented and discussed. For moderate values of the bilayer splitting (Delta E comparable to 2Delta_{max}) the spectra of the superconducting state exhibit an additional mode which is due to the condensate and similar to the one of earlier phenomenological approaches.