Investigation of Precursor Superconducting State in YBa$_2$Cu$_3$O$_{7-\delta}$ through In-plane Optical Spectroscopy

TL;DR

This study investigates the presence of precursor superconductivity in underdoped YBa₂Cu₃O₇−δ using in-plane optical spectroscopy, confirming intrinsic precursor phenomena above the critical temperature.

Contribution

It provides direct in-plane optical evidence of precursor superconductivity in underdoped cuprates, aligning with previous c-axis findings and confirming its intrinsic nature.

Findings

Superconducting response detected in in-plane spectra above T_c

Precursor superconductivity is intrinsic in underdoped cuprates

Optical spectroscopy confirms precursor phenomena consistent with c-axis data

Abstract

A precursor of superconductivity has been searched in the in-plane optical spectra of underdoped YBa$_2$Cu$_3$O$_y$, in which the previous $c$-axis optical spectra showed the presence of superconducting carriers at a temperature far above $T_c$ [Uykur $et al$., Phys. Rev. Lett. 112, 127003 (2014)][Dubroka $et al$., Phys. Rev. Lett. 106, 047006 (2011)]. By carefully subtracting the normal component from the imaginary part of conductivity $\sigma_2$($\omega$), we found a clear in-plane response of superconducting condensate at the temperature consistent with the $c$-axis optical data. This confirms that the precursory superconductivity developing with reducing a doping level is an intrinsic phenomenon in the cuprates.