High-Tc superconductivity and antiferromagnetism in multilayer cuprates: 63Cu- and 19F-NMR on five-layer Ba2Ca4Cu5O10(F,O)2

TL;DR

This study uses NMR to explore the coexistence of antiferromagnetism and superconductivity in multilayer cuprates, revealing how interlayer coupling influences phase diagrams and high critical temperatures.

Contribution

It provides the first detailed layer-dependent phase diagram of AFM and SC in five-layer cuprates, linking interlayer magnetic coupling to the evolution of high-Tc superconductivity.

Findings

AFM coexists with SC in underdoped regions.

Critical hole density pc increases with the number of layers.

Maximum Tc is near the quantum critical point where AFM collapses.

Abstract

We report systematic Cu- and F-NMR measurements of five-layered high-Tc cuprates Ba2Ca4Cu5O10(F,O)2. It is revealed that antiferromagnetism (AFM) uniformly coexists with superconductivity (SC) in underdoped regions, and that the critical hole density pc for AFM is ~ 0.11 in the five-layered compound. We present the layer-number dependence of AFM and SC phase diagrams in hole-doped cuprates, where pc for n-layered compounds, pc(n), increases from pc(1) ~ 0.02 in LSCO or pc(2) ~ 0.05 in YBCO to pc(5) ~ 0.11. The variation of pc(n) is attributed to interlayer magnetic coupling, which becomes stronger with increasing n. In addition, we focus on the ground-state phase diagram of CuO2 planes, where AFM metallic states in slightly doped Mott insulators change into the uniformly mixed phase of AFM and SC and into simple d-wave SC states. The maximum Tc exists just outside the quantum critical hole density, at which AFM moments on a CuO2 plane collapse at the ground state, indicating an intimate relationship between AFM and SC. These characteristics of the ground state are accounted for by the Mott physics based on the t-J model; the attractive interaction of high-Tc SC, which raises Tc as high as 160 K, is an in-plane superexchange interaction Jin (~ 0.12 eV), and the large Jin binds electrons of opposite spins between neighboring sites. It is the Coulomb repulsive interaction U ~ (> 6 eV) between Cu-3d electrons that plays a central role in the physics behind high-Tc phenomena.