Hole superconductivity from kinetic energy gain

The apparently unrelated experimental observations of optical sum rule viol ation(1) and of tunneling asymmetry in NIS tunneling(2) find a simple expla nation within the theory of hole superconductivity. In fact, both phenomena were predicted by the theory long before they were experimentally observed (3,4). Other experimental predictions of the theory, in particular a novel feature expected in photoemission experiments, are discussed.