Doping dependence of the superconducting gap in Tl_2Ba_2CuO_{6+delta} from heat transport

TL;DR

This study measures the superconducting gap in Tl_2Ba_2CuO_{6+delta} across doping levels using heat transport, revealing a decreasing gap with doping and supporting a pure d-wave superconducting state.

Contribution

It provides the first bulk thermal conductivity measurements of the superconducting gap across the overdoped regime in Tl_2Ba_2CuO_{6+delta}, confirming the d-wave symmetry and its doping dependence.

Findings

Superconducting gap decreases with increased doping.

Gap-to-Tc ratio increases as hole concentration decreases.

Superconducting state remains pure d-wave into the underdoped regime.

Abstract

We present low-temperature thermal conductivity measurements on the cuprate Tl_2Ba_2CuO_{6+delta} throughout the overdoped regime. In the T -> 0 limit, the thermal conductivity due to d-wave nodal quasiparticles provides a bulk measurement of the superconducting gap, Delta. We find Delta to decrease with increasing doping, with a magnitude consistent with spectroscopic measurements (photoemission and tunneling). This argues for a pure and simple d-wave superconducting state in the overdoped region of the phase diagram, which appears to extend into the underdoped regime down to a hole concentration of 0.1 hole/Cu. As hole concentration is decreased, the gap-to-Tc ratio increases, showing that the suppression of the superconducting transition temperature Tc (relative to the gap) begins in the overdoped regime.