New Josephson Plasma Modes in Underdoped YBa2Cu3O6.6 Induced by Parallel Magnetic Field

TL;DR

This study reveals new Josephson plasma modes in underdoped YBa2Cu3O6.6 induced by a parallel magnetic field, showing how magnetic fields alter interlayer coupling and spectral weight distribution.

Contribution

It demonstrates the emergence of a new optical Josephson mode and changes in Josephson coupling strengths under parallel magnetic fields in underdoped YBCO.

Findings

A new peak appears in the optical conductivity spectrum under magnetic field.

Spectral weight shifts from the condensate to intra-bilayer and Josephson modes.

The c-axis condensate weight is redistributed by the magnetic field.

Abstract

The c-axis reflectivity spectrum of underdoped YBa2Cu3O6.6 (YBCO) is measured below Tc=59K in parallel magnetic fields H//CuO2 up to 7T. Upon application of a parallel field, a new peak appears at finite frequency in the optical conductivity at the expense of suppression of c-axis condensate weight. We conclude that the dramatic change originates from different Josephson coupling strengths between bilayers with and without Josephson vortices. We find that the 400cm^-1 broad conductivity peak in YBCO gains the spectral weight under parallel magnetic field; this indicates that the condensate weight at \omega =0 is distributed to the intra-bilayer mode as well as to the new optical Josephson mode.