Frustrated kinetic energy, the optical sum rule, and the mechanism of superconductivity

The basis of the interlayer tunneling theory of high-temperature supercondu ctivity is that the electronic kinetic energy in a direction perpendicular to the copper-oxygen planes is a substantial fraction of the condensation e nergy. This issue is critically examined, and it is argued from a rigorous conductivity sum rule that the consequences of this theory are consistent w ith recent optical and penetration depth measurements.