Unconventional energetics of the pseudogap state and superconducting state in high-Tc cuprates -: art. no. 134514

Insight into the nature of the pairing of charge carriers in high-T-c superconductors may be provided by a systematic investigation of the condensation energy. In this work we report on studies of the electronic kinetic energy across the complex phase diagram of these materials. The c-axis component of the electronic kinetic energy (determined from an analysis of the optical constants) is shown to be reduced below T-c, primarily in those compounds in which the superconducting transition at T-c is preceded by the formation of the partial gap in the density of states (pseudogap) at T*>T-c. An examination of the doping dependence of the infrared conductivity in conjunction with the results of photoemission spectroscopy suggests that the lowering of the kinetic energy is a property of the electronic states close to the intersection of the two-dimensional Fermi surface with the boundary of the Brillouin zone. We contrast the c-axis results with the energetics associated with the nodal quasiparticles probed through the in-plane conductivity.