Hidden order in the cuprates - art. no. 094503

We propose that the enigmatic pseudogap phase of cuprate superconductors is characterized by a hidden broken symmetry of d(x2-y2)-type. The transition to this state is rounded by disorder, but in the limit that the disorder i s made sufficiently small, the pseudogap crossover should reveal itself to be such a transition. The ordered state breaks time-reversal, translational , and rotational symmetries, but it is invariant under the combination of a ny two. We discuss these ideas in the context of ten specific experimental properties of the cuprates, and make several predictions, including the exi stence of an as-yet undetected metal-metal transition under the superconduc ting dome.