High-TcSuperconductivity and Antiferromagnetism in Multilayered Copper Oxides –A New Paradigm of Superconducting Mechanism–

Abstract

High-temperature superconductivity (HTSC) in copper oxides emerges on a layered CuO 2 plane when an antiferromagnetic Mott insulator is doped with mobile hole carriers. We review extensive studies of multilayered copper oxides by site-selective nuclear magnetic resonance (NMR), which have uncovered the intrinsic phase diagram of antiferromagnetism (AFM) and HTSC for a disorder-free CuO 2 plane with hole carriers. We present our experimental findings such as the existence of the AFM metallic state in doped Mott insulators, the uniformly mixed phase of AFM and HTSC, and the emergence of d -wave SC with a maximum T c just outside a critical carrier density, at which the AFM moment on a CuO 2 plane disappears. These results can be accounted for by the Mott physics based on the t – J model. The superexchange interaction J in among spins plays a vital role as a glue for Cooper pairs or mobile spin-singlet pairs, in contrast to the phonon-mediated attractive interaction among electrons established in the Bardeen–Cooper–Schrieffer (BCS) theory. We remark that the attractive interaction for raising the T c of HTSC up to temperatures as high as 160 K is the large J in (∼0.12 eV), which binds electrons of opposite spins to be on neighboring sites, and that there are no bosonic glues. It is the Coulomb repulsive interaction U (> 6 eV) among Cu-3 d electrons that plays a central role in the physics behind high- T c phenomena. A new paradigm of the SC mechanism opens to strongly correlated electron matter.