Doping dependence of superconducting gap in YBa2Cu3Oy from universal heat transport

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 2 Cu 3 O y . The residual linear term κ 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 κ 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.