Interlayer conductivity in the superconductor Tl2Ba2CuO6+delta: Energetics and energy scales

We report on infrared studies of the c-axis electrodynamics of Tl2Ba2CuO6+delta crystals. A sum-rule analysis reveals spectral weight shifts that can be interpreted as a kinetic energy change at the superconducting transition. In optimally doped crystals, showing an incoherent normal-state response, the kinetic energy is lowered at TT-c.