Energy Gap Structure in Bilayer Oxide Superconductors

TL;DR

This paper models bilayer oxide superconductors with coexisting interlayer and intralayer d-wave pairing, explaining experimental node splitting and predicting new symmetry-breaking phenomena and Raman modes.

Contribution

It introduces a novel bilayer superconductor model with coexisting pairing amplitudes, explaining experimental observations and predicting spontaneous symmetry breaking and new collective modes.

Findings

Explains the splitting of energy gap nodes observed in experiments.

Predicts spontaneous breaking of tetragonal symmetry.

Identifies a new Raman active mode due to out-of-phase oscillations.

Abstract

We consider a model for bilayer superconductors where an interlayer pairing amplitude $\Delta_\perp$ co-exists with intralayer pairing $\Delta_\|$ 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 $\Delta_\perp$ and $\Delta_\|$ gives rise to a new Raman active mode. The phase of $\Delta_\perp$ may also become imaginary, leading to a state which breaks time reversal symmetry, which may have important implications for tunnelling experiments.