J.E. Hirsch and F. Marsiglio, cond-mat/9908322 (Los Alamos) ,Physica C 331, 150 (2000).
Anderson's interlayer tunneling model can account for up to 1% of the condensation energy of Tl_2Ba_2CuO_y. Here we account for the remaining 99%. We predict an in-plane kinetic energy gain of 1 to 3 meV per planar oxygen in the optimally doped material when it goes superconducting. It is suggested that the effect may be most easily detected in underdoped dirty samples.