Twin boundaries in orthorhombic d-wave superconductors were investigated numerically by using the Bogoliubov-deGennes formalism within the context of an extended Hubbard model. The twin boundaries were represented by tetragonal regions of variable width, with a reduced chemical potential. For sufficiently large twin boundary widths and changes in chemical potential, an induced s-wave component could break time-reversal symmetry at a low temperature. This temperature, and the magnitude of the imaginary component, were found to depend strongly upon the electron density.

D.L.Feder, A.Beardsall, A.J.Berlinsky, C.Kallin: Physical Review B, 1997, 56[10], R5751-4