Temperature dependence of the bulk energy gap in underdoped Bi-2212: Evidence for the mean-field superconducting transition

TL;DR

This study uses advanced spectroscopy to show that the superconducting transition in underdoped Bi-2212 follows a mean-field BCS-like behavior, with the gap opening abruptly and the critical temperature peaking at optimal doping.

Contribution

It provides clear spectroscopic evidence that the superconducting transition in underdoped Bi-2212 is mean-field-like, challenging theories linking superconductivity closely with antiferromagnetic gaps.

Findings

Superconducting transition maintains mean-field character down to moderate underdoping.

Superconducting gap opens abruptly at the transition temperature.

Critical temperature peaks at optimal doping and decreases with underdoping.

Abstract

Understanding of the puzzling phenomenon of high temperature superconductivity requires reliable spectroscopic information about temperature dependence of the bulk electronic density of states. Here I present a comprehensive analysis of $T-$evolution of bulk electronic spectra in Bi-2212 obtained by Intrinsic Tunneling Spectroscopy on small mesa structures. Unambiguous spectroscopic information is obtained by obviation of self-heating problem and by improving the spectroscopic resolution. The obtained data indicate that the superconducting transition maintains the mean-field character down to moderate underdoping, and is associated with an abrupt opening of the superconducting gap, which is well described by the conventional BCS $T-$dependence. The mean-field critical temperature reaches maximum at the optimal doping and decreases with underdoping. Such behavior is inconsistent with theories assuming intimate connection between superconducting and antiferromagnetic spin gaps, and support proposals associating high temperature superconductivity with the presence of competing ground states and a quantum critical point near optimal doping.