Time Reversal Symmetry Breaking States Near Grain Boundaries Between   d-wave Superconductors
  In this paper we study the order parameter and density of states near a grain boundary between two $d_{x^2-y^2}$ superconductors. We examine broken time reversal symmetry near the interface. In particular we show that, under suitable circumstances, time reversal symmetry must be broken even when the order parameter is purely $d_{x^2-y^2}$ everywhere in space. 
M. Fogelstrom and S.-K. Yip