9 research outputs found
Electronic States and Superconductivity in Multi-layer High-Tc Cuprates
We study electronic states of multilayer cuprates in the normal phases as
functions of the number of CuO_2 planes and the doping rate. The resonating
valence bond wave function and the Gutzwiller approximation are used for a
two-dimensional multilayer t-t'-t''-J model. We calculate the electron-removal
spectral functions at (\pi,0) in the CuO_2 plane next to the surface to
understand the angle-resolved photoemission spectroscopy (ARPES) spectra. We
find that the trilayer spectrum is narrower than the bilayer spectrum but is
wider than the monolayer spectrum. In the tri- and tetralayer systems, the
outer CuO_2 plane has different superconducting amplitude from the inner CuO_2
plane, while each layer in the bilayer systems has same amplitude. The recent
ARPES and NMR experiments are discussed in the light of the present theory.Comment: 7 pages, 7 figure
High-Tc Superconductivity and Antiferromagnetism in Multilayered Copper Oxides - A New Paradigm of Superconducting Mechanism -
High-temperature superconductivity (HTSC) in copper oxides emerges on a
layered CuO2 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 CuO2 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 Tc just outside a critical carrier density, at which
the AFM moment on a CuO2 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 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-3d
electrons that plays a central role in the physics behind high-Tc phenomena. A
new paradigm of the SC mechanism opens to strongly correlated electron matter.Comment: 20 pages, 25 figures, Special topics "Recent Developments in
Superconductivity" in J. Phys. Soc. Jpn., Published December 26, 201