Spontaneous vortex phase in the bosonic resonating valence bond theory

Abstract

In the description of spin-charge separation based on the phase string theory of the $t\ensuremath{-}J$ model, spinon excitations are vortices in the superconducting state. Thermally excited spinons destroy phase coherence, leading to a new phase characterized by the presence of free spinon vortices at temperatures ${T}_{c}<T<{T}_{v}.$ The temperature scale ${T}_{v}$ at which holon condensation occurs marks the onset of the pairing amplitude and is related to the spin-pseudogap temperature ${T}^{*}.$ The phase below ${T}_{v},$ called the spontaneous vortex phase, shows novel transport properties before phase coherence sets in at ${T}_{c}.$ We discuss the Nernst effect as an intrinsic characterization of such a phase, in comparison with recent experimental measurements.