Non-BCS Superconductivity in Cuprates from Attraction of Spin Vortices

Abstract

We propose a non-BCS mechanism for superconductivity (SC) in hole-underdoped cuprates based on a gauge approach to the t-J model. The gluing force is a long-range attraction between spin vortices centered on the empty sites of two opposite Néel sublattices, leading to pairing of charge carriers (spinless holons). In the presence of these pairs, a gauge force coming from the single occupancy constraint induces, in turn, a RVB pairing of the spin carriers (spinons), gapped by scattering against spin-vortices. This gives rise to a finite density of incoherent hole pairs, precursor to superconductivity, supporting a Nernst signal whose anticipated contour plot is qualitatively consistent with experiments. The true superconducting transition occurs at an even lower temperature via a planar XY-type transition and it involves a kinetic energy gain due to lowering of the spinon gap. Since the short-range antiferromagnetic (AF) order and the holon pairing originate from the same term of the t-J model, this approach incorporates a strong interplay between AF and SC, giving rise to a universal relation between the energy of the resonance mode (bound state of spinons) and Tc, as observed in neutron scattering experiments.