Spin-gap proximity effect mechanism of high-temperature superconductivity

Abstract

When holes are doped into an antiferromagnetic insulator they form a slowly fluctuating array of ``topological defects'' (metallic stripes) in which the motion of the holes exhibits a self-organized quasi-one-dimensional electronic character. The accompanying lateral confinement of the intervening Mott-insulating regions induces a spin gap or pseudogap in the environment of the stripes. We present a theory of underdoped high-temperature superconductors and show that there is a local separation of spin and charge and that the mobile holes on an individual stripe acquire a spin gap via pair hopping between the stripe and its environment, i.e., via a magnetic analog of the usual superconducting proximity effect. In this way a high pairing scale without a large mass renormalization is established despite the strong Coulomb repulsion between the holes. Thus the mechanism of pairing is the generation of a spin gap in spatially confined Mott-insulating regions of the material in the proximity of the metallic stripes. At nonvanishing stripe densities, Josephson coupling between stripes produces a dimensional crossover to a state with long-range superconducting phase coherence. This picture is established by obtaining exact and well-controlled approximate solutions of a model of a one-dimensional electron gas in an active environment. An extended discussion of the experimental evidence supporting the relevance of these results to the cuprate superconductors is given.