Magnetic fluctuations in coupled inequivalent Hubbard layers as a model for Y2Ba4Cu7O15

TL;DR

This study models magnetic fluctuations in coupled inequivalent Hubbard layers to understand Y2Ba4Cu7O15, revealing how interlayer magnetic coupling influences magnetic properties and charge carrier behavior, aligning with experimental NMR data.

Contribution

It introduces a correlated-electron model with inequivalent Hubbard layers and analyzes interlayer magnetic effects, providing new insights into magnetic and charge dynamics in Y2Ba4Cu7O15.

Findings

Interlayer magnetic coupling causes magnetic property equalization between layers.

Antiferromagnetic fluctuations are suppressed in less doped and enhanced in heavily doped layers.

The model's results agree with NMR experiments on Y2Ba4Cu7O15.

Abstract

We investigate, within the fluctuation-exchange approximation, a correlated-electron model for Y2Ba4Cu7O15 represented by two inequivalent Hubbard layers coupled by an interlayer hopping $t_\perp$. An energy offset $\delta$ is introduced in order to produce a different charge carrier concentration in the two layers. We compare several single-particle and magnetic excitations, namely, the single particle scattering rate, the spectral function and the spin lattice as well as spin-spin relaxation times in the two layers as a function of $\delta$. We show that the induced interlayer magnetic coupling produces a tendency to ``equalization'' of the magnetic properties in the two layers whereby antiferromagnetic fluctuations are suppressed in the less doped layer and enhanced in the heavily doped one. The strong antiferromagnetic bilayer coupling causes the charge carriers in the plane with larger doping concentration to behave similar to those of the underdoped layer, they are coupled to. This effect grows for decreasing temperature. For high temperatures or if both layers are optimally or overdoped, i.e. when the antiferromagnetic correlation length becomes of the order or smaller than one lattice site the charge carrier and magnetic dynamics of the two layers is disconnected and the equalization effect disappears. These results are in good agreement with NMR experiments on Y2Ba4Cu7O15 by Stern et al. [Phys. Rev B 51, 15478 (1995)]. We also compare the results with calculations on bilayer systems with equivalent layers as models for the constituent compounds YBa2Cu3O7 and YBa2Cu4O8.