Role of Spinon Excitations on KT Transition at Low Energies in d-Wave Superconductors

By using a low energy effective Lagrangian of the U(1) slave boson mean field theory we examine the vortex binding-unbinding transition (KT transition) from a doped Mott insulator at low temperatures in a d-wave superconductor. It is shown that the interaction potential between vortices is modified by a "Doppler energy shift" resulting in additional attractive interaction, as a consequence of supercurrent fluctuations coupled to the particle-hole excitations of the massless Dirac fermions.