Fractional Vortices as Evidence of Time-Reversal Symmetry Breaking in   High-Temperature Superconductors
  We argue that recent experiments by Kirtley et al. may show evidence of time reversal symmetry breaking in YBCO at crystal grain boundaries. We illustrate this through a Ginzburg-Landau model calculation. Further experimental tests are proposed. 
M. Sigrist, D. B. Bailey and R. B. Laughlin