Quantitative test of a microscopic mechanism of high-temperature superconductivity

One of the main challenges to theoretical attempts to understand the micros copic mechanism of high-transition-temperature (high-T-c) superconductivity is to account quantitatively for the superconducting condensation energy, the energy by which the normal state differs from the superconducting state (1-6). A microscopic model commonly used to describe the superconducting co pper oxides, the t-J model(7), is thought to capture the essential physics of the phenomenon: the interplay between the electrons' kinetic energy and their antiferromagnetic exchange interaction. Within the t-J model the cond ensation energy can be related to the change in the dynamical spin structur e between the superconducting and the normal states(8). Here we propose a m icroscopic mechanism for the condensation energy of high-T-c superconductor s. Within this mechanism, the appearance of a resonance in the superconduct ing state(9-13) enables the antiferromagnetic exchange energy in this state to be lowered relative to the normal state. We show that the intensity of the resonant neutron-scattering peak observed previously in YBa2Cu3O7 when it undergoes the transition to the superconducting state(14-16) is in quant itative agreement with the condensation energy of these materials(2,3).