Time-Reversal Symmetry Breaking: an Evidence for Spin Pairingin High-T_c Superconductors

Effective spin coupling leads to local triplet pairing in the antiferromagnetically ordered CuO₂ plane as shown by the K-J model Guo et al. Chin. Phys. Lett. 18 (2001) 103. The precession of the spin triplet(S=1, S_z = 0) in the CuO₂ plane does not hold time-reversal invariance due to the dimpled CuO structure, which not only modifies the gap function but also contributes to the asymmetry of the high-T_c tunneling conductance. In principle, the effect of time-reversal symmetry breaking can be manifested by the variation of the conductance asymmetry by applying a magnetic field at superconductor-insulator-normal metal junction, which should provide a direct evidence for triplet pairing in the high-T_c superconductors.