Energy gap structure in bilayer oxide superconductors

Abstract

We consider a model for bilayer superconductors where an interlayer pairing amplitude Δ ⊥ coexists with intralayer pairing Δ ∥ of d x 2− y 2 symmetry. This model is motivated by a recent photoemission experiment reporting the splitting of the nodes of the energy gap. In addition to offering a natural explanation of this observation, the model has a number of new experimental consequences. We find that the new state is accompanied by a spontaneous breaking of the tetragonal symmetry. We also find that the out-of-phase oscillation of Δ ⊥ and Δ ∥ gives rise to a new Raman active mode. The phase of Δ ⊥ may also become imaginary, leading to a state which breaks time reversal symmetry, which may have important implications for tunnelling experiments.