a-b plane optical conductivity in YBa_2Cu_3O_{7-delta} above and below T*

TL;DR

This study investigates the a-b plane optical conductivity in YBa2Cu3O7-delta, revealing a spectral dip below T* linked to inhomogeneous charge distribution and suggesting preformed pairs undergo Bose-Einstein condensation.

Contribution

It provides new insights into the spectral features and carrier behavior in YBa2Cu3O7-delta, proposing a model involving inhomogeneous carriers and preformed pairs below T*.

Findings

A dip in optical conductivity spectrum appears below T*.

Spectral changes coincide with phonon anomalies.

Data supports inhomogeneous charge distribution and preformed pairs.

Abstract

Analysis of the a-b plane optical conductivity $\sigma_{ab}$ for both twinned and untwinned YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ as a function of temperature and doping shows that below a well defined temperature T*, a dip in the spectrum systematically appears separating the infrared charge excitation spectrum into two components with distinct energy scales. The change from monotonic behaviour in $\sigma_{ab}$ is found to be concurrent with the onset of phonon anomalies in Raman and infrared spectra below T*. The optical data are suggested to be evidence for the appearance of an inhomogeneous distribution of carriers rather than the opening of a simple gap for charge excitations below T*, an interpretation wich is consistent with recent angle-resoved photoemission and electronic Raman spectra. We find that the behaviour below T* and the absence of any anomalies at Tc can be interpreted assuming a Bose-Einstein condensation of preformed pairs.