Specific-Heat Measurement of Residual Superconductivity in the Normal State of Underdoped Cuprate Superconductors

TL;DR

This study investigates the residual superconductivity in underdoped cuprate superconductors by measuring specific heat across various doping levels, revealing persistent superconducting signatures above the critical temperature.

Contribution

It provides the first detailed analysis of specific heat behavior in underdoped cuprates, demonstrating residual superconductivity above T_c through entropy conservation.

Findings

Residual superconductivity persists above T_c in underdoped samples.

Specific heat coefficient shows a long tail into the normal state for underdoped samples.

Entropy associated with superconductivity is conserved when considering the long tail.

Abstract

We have measured the magnetic field and temperature dependence of specific heat on $Bi_2Sr_{2-x}La_xCuO_{6+\delta}$ single crystals in wide doping and temperature regions. The superconductivity related specific heat coefficient $\gamma_{sc}$ and entropy $S_{sc}$ are determined. It is found that $\gamma_{sc}$ has a hump-like anomaly at $T_c$ and behaves as a long tail which persists far into the normal state for the underdoped samples, but for the heavily overdoped samples the anomaly ends sharply just near $T_c$. Interestingly, we found that the entropy associated with superconductivity is roughly conserved when and only the long tail part in the normal state is taken into account for the underdoped samples, indicating the residual superconductivity above T$_c$.