Role of spinon in the presence of spinon singlet pair excitations on phase transitions in d-wave superconductors

摘要

We examine the roles of massless Dirac spinon and spin singlet pair excitations on both quantum and classical phase transitions in extreme type-II d-wave superconductors. We discuss that the massless Dirac fermion (spinon) excitations in the presence of the spin singlet pair excitations do not alter the nature of the quantum phase transition at T = 0, that is, the XY universality class, while at finite temperature they are seen to induce an additional logarithmic interaction potential between vortices, further stabilizing vortex-antivortex pairs at low temperature for KT transition for lightly doped high-T_c samples.