Proposal for an experiment to test a theory of high-temperature superconductors

A theory for the phenomena observed in copper-oxide based high-temperature superconducting materials derives an elusive time-reversal and rotational s ymmetry-breaking order parameter for the observed pseudogap phase ending at a quantum-critical point near the composition for the highest T-c. An expe riment is proposed to observe such a symmetry breaking. It is shown that an gle-resolved photoemission yields a current density which is different for left and right circularly polarized photons. The magnitude of the effect an d its momentum dependence is estimated. Barring the presence of domains of the predicted phase, an asymmetry of about 0.1 is predicted at low temperat ures in moderately underdoped samples.