Doping dependence of superconducting gap in YBa_2Cu_3O_y from universal heat transport

TL;DR

This study investigates how the superconducting gap in YBa_2Cu_3O_y varies with doping by measuring thermal transport at very low temperatures, revealing a close relationship with the pseudogap and implications for the phase diagram.

Contribution

It provides the first detailed doping-dependent analysis of the superconducting gap via heat transport, linking it to the pseudogap and challenging certain quantum phase transition theories.

Findings

Residual linear thermal conductivity decreases with underdoping.

Superconducting gap scales with the pseudogap across doping levels.

Linear term presence suggests no complex order parameter transition.

Abstract

Thermal transport in the T -> 0 limit was measured as a function of doping in high-quality single crystals of the cuprate superconductor YBa_2Cu_3O_y. The residual linear term kappa_0/T is found to decrease as one moves from the overdoped regime towards the Mott insulator region of the phase diagram. The doping dependence of the low-energy quasiparticle gap extracted from kappa_0/T is seen to scale closely with that of the pseudogap, arguing against a non-superconducting origin for the pseudogap. The presence of a linear term for all dopings is evidence against the existence of a quantum phase transition to an order parameter with a complex (ix) component.