Unusual Nernst Effect Suggesting Time-Reversal Violation in the Striped Cuprate Superconductor La2-xBaxCuO4

The striped cuprate La2-xBaxCuO4 (x = 1/8) undergoes several transitions below the charge-ordering temperature T-co 54 K. From Nernst experiments, we find that, below T-co, there exists a large, anomalous Nernst signal e(N.even)(H, T) that is symmetric in field H, and remains finite as H -> 0. The time-reversal violating signal suggests that, below T-co, vortices of one sign are spontaneously created to relieve interlayer phase frustration.