BEREZINSKII-KOSTERLITZ-THOULESS TRANSITION IN A SPIN-CHARGE-SEPARATED SUPERCONDUCTOR

A model for spin-charge-separated superconductivity in two dimensions is introduced where the phases of the spinon and holon order parameters couple guage invariantly to a statistical gauge field representing chiral spin fluctuations. The model is analyzed in the continuum limit and in the low-temperature limit. In both cases we find that physical electronic phase correlations show a superconducting-normal phase transition of the Berezinskii-Kosterlitz-Thouless type, while statistical gauge-field excitations are found to be strictly gapless. It is argued that the former transition is in the same universality class as that of the XY model. We thus predict a universal jump in the superfluid density at this transition. The normal-to-superconductor phase boundary for this model is also obtained as a function of carrier density, where we find that its shape compares favorably with that of the experimentally observed phase diagram for the oxide superconductors.