Coexistence of the Pseudogap and the Superconducting Gap Revealed by the \textit{c}-axis Optical Study of YBa$_{2}$(Cu$_{1-x}$Zn$_{x}$)$_{3}$O$_{7-\delta}$

TL;DR

This study uses c-axis optical spectroscopy to show that in underdoped YBa2(Cu1-xZnx)3O7-δ, the pseudogap coexists with the superconducting gap, and the pseudogap persists even in non-superconducting samples, challenging its role as a precursor to superconductivity.

Contribution

It provides direct optical evidence of the coexistence of pseudogap and superconducting gap and demonstrates the pseudogap's independence from superconductivity in cuprates.

Findings

Spectral weight transfer to high energy persists below Tc in Zn-doped samples.

Pseudogap observed even in non-superconducting Zn-doped samples.

Pseudogap is not a precursor to superconductivity.

Abstract

To address the issue of the pseudogap in the superconducting state of the high temperature superconducting cuprates, we studied the temperature dependent redistribution of the spectral weight in the \textit{c}-axis polarized optical spectra for underdoped YBa$_{2}$(Cu$_{1-x}$Zn$_{x}$)$_{3}$O$_{7-\delta}$ single crystals with $x=0,0.007,$ 0.012, and 0.04. It was found that for Zn substituted samples, the spectral weight transfer to the high energy region, which characterizes the pseudogap state, continues even below the superconducting transition temperature (\textit{T}$_{c}$), indicating the coexistence of the pseudogap and the superconducting gap. Moreover, the observation of the pseudogap in the Zn-doped non-superconducting sample gives evidence that the pseudogap is not a precursor of superconductivity.