Quantitative test of a microscopic mechanism of high-temperature superconductivity

One of the main challenges to theoretical attempts to understand the microscopic 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 state1,2,3,4,5,6. A microscopic model commonly used to describe the superconducting copper oxides, the t - J model7, 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 condensation energy can be related to the change in the dynamical spin structure between the superconducting and the normal states8. Here we propose a microscopic mechanism for the condensation energy of high- T c superconductors. Within this mechanism, the appearance of a resonance in the superconducting state9,10,11,12,13 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 state14,15,16 is in quantitative agreement with the condensation energy of these materials2,3.