Spontaneous Time Reversal Symmetry Breaking in the Pseudogap State of High-Tc Superconductors

Here, using angle-resolved photoemission with circularly polarized light, we find that, in the pseudogap state, left-circularly polarized photons give a different photocurrent than right-circularly polarized photons, and therefore the state below T* is rather unusual, in that it breaks time reversal symmetry. This may indicate a magnetic origin of the pseudogap phase of high-Tc superconductors.