Negative superfluid densities in superconducting films in a parallel   magnetic field
  In this paper we develop a theory of mesoscopic fluctuations in disordered thin superconducting films in a parallel magnetic field. At zero temperature and sufficiently strong magnetic field the system undergoes a phase transition into a state characterized by a superfluid density, which is random in sign. Consequently, in this region, random supercurrents are spontaneously created in the ground state of the system, and it belongs to the same universality class as the two dimensional XY spin glass with a random sign of the exchange interaction. 
F. Zhou(Princeton University), B. Spivak (University of Washington)