Charge inhomogeneity and high temperature superconductivity

When charge is doped into a correlated insulator, it forms an inhomogeneous state which may be fluctuating, ordered or glassy. The outstandingly successful BCS theory of superconductivity was not designed for doped insulators, and an appropriate theory must incorporate the local electronic structure on the scale of the superconducting coherence length. Unlike conventional materials, superconductivity in the cuprates is driven by lowering the in-plane zero-point kinetic energy. There is extensive experimental evidence in support of this picture. Inelastic X-ray scattering can give information about the existence and energy scale of the charge structure, especially in optimally doped materials. (C) 2000 Published by Elsevier Science Ltd.