Detecting dichroism in angle-resolved photoemission

Recently, the time-reversal violation predicted for the pseudogap phase of the cuprates, which was observed by dichroism experiments using angle-resolved photoemission, has also been observed by polarized neutron diffraction. The earlier derivation of dichroism in angle-resolved photoemission due to time-reversal violation relied on the existence of mirror planes in the crystal. Here the theory of the effect is generalized to the case that mirror plane symmetry is weakly violated due to perturbing potentials such as a superstructure.