Interlayer Tunneling Models of Cuprate Superconductivity: Implications of a Recent Experiment

It is shown that, given a few generic assumptions, any theory of high-temperature superconductivity that attributes a substantial fraction of the condensation energy to the saving of c -axis kinetic energy must predict an inequality relating the c -axis penetration depth λ ⊥ (0) to the zero-temperature superconducting-normal energy difference and the fluctuations of the c -axis kinetic energy around its mean value. Application of this formula to Tl 2 Ba 2 CuO 6 implies that if λ ⊥ (0) is greater than 10 micrometers, as suggested by a recent experiment, these fluctuations must have an unusual form.