On Vortices and Phase Coherence in High Tc Superconductors

TL;DR

This paper proposes that high Tc superconductors exhibit topological order with vortex-antivortex dynamics, rather than traditional phase coherence, explaining various experimental phenomena above the critical temperature.

Contribution

It introduces a topological order framework for high Tc superconductors, emphasizing vortex behavior and phase fluctuations over conventional phase coherence.

Findings

High Tc cuprates are topologically ordered superconductors.

Vortex-antivortex unbinding governs the transition temperature in underdoped cuprates.

Vortices above Tc cause flux flow and Nernst effects, with a measurable depairing field.

Abstract

We show that an array of Josephson coupled Cooper paired planes can never have long range phase coherence at any finite temperature due to an infrared divergence of phase fluctuations. The phase correlations decay in a slow enough manner providing enough local phase coherence as to make possible the nucleation of vortices. The planes then acquire Kosterlitz-Thouless topological order with its intrinsic rigidity and concomitant superfluidity. We thus conclude that the high temperature superconducting cuprates are topologically ordered superconductors rather than phase ordered superconductors. For low enough superfluid densities, as in the underdoped cuprates, the transition temperature, Tc, will be proportional to the superfluid density corresponding to vortex-antivortex unbinding, and not to disappearance of the Cooper pairing amplitude. Above Tc, but below the BCS pairing temperature Tp, we will have a dephased Cooper pair fluid that is a vortex-antivortex liquid. The AC and DC conductivities measured in this region are those corresponding to flux flow. Furthermore there will be vortices above Tc which will lead to Nernst vortexlike response and there will be a measurable depairing field H_c2 above Tc as evidenced by recent experiments.