Vortex-pair unbinding in the normal state of two-dimensional, short   coherence-length superconductors
  We study the superconducting transition in the attractive Hubbard model in two dimensions using the self-consistent $T$-matrix approximation. We demonstrate that for large system sizes, this approximate method produces XY critical scaling in the correlation length and pair susceptibility. For the parameters we investigate, the critical regime is quite large, extending beyond 5 times $\TKTB$. We discuss the role of vortex-pair unbinding in the normal state in the context of pseudogap behaviour and the relevance to the physics of underdoped cuprates. 
Jan R. Engelbrecht and Alexander B. Nazarenko (Boston College)