Effects of intrabilayer coupling on the magnetic properties of YBa$_2$Cu$_3$O$_6$

TL;DR

This study uses quantum Monte Carlo simulations on a two-layer Heisenberg model to analyze how intrabilayer coupling influences magnetic properties of YBa₂Cu₃O₆, revealing that even weak coupling significantly enhances correlations at high temperatures.

Contribution

It provides the first detailed quantum Monte Carlo analysis of intrabilayer coupling effects on magnetic properties in bilayer cuprates.

Findings

Increasing intrabilayer coupling enhances magnetic correlations at high temperatures.

Even small coupling ratios significantly affect the NMR spin-echo decay rate.

High-temperature measurements of $1/T_{2G}$ can estimate intrabilayer coupling strength.

Abstract

A two-layer Heisenberg antiferromagnet is studied as a model of the bilayer cuprate YBa$_2$Cu$_3$O$_6$. Quantum Monte Carlo results are presented for the temperature dependence of the spin correlation length, the static structure factor, the magnetic susceptibility, and the $^{63}$Cu NMR spin-echo decay rate $1/T_{2G}$. As expected, when the ratio $J_2/J_1$ of the intrabilayer and in-plane coupling strengths is small, increasing $J_2$ pushes the system deeper inside the renormalized classical regime. Even for $J_2/J_1$ as small as $0.1$ the correlations are considerably enhanced at temperatures as high as $T/J_1 \approx 0.4-0.5$. This has a significant effect on $1/T_{2G}$, and it is suggested that measurements of this quantity at high temperatures can reveal the strength of the intrabilayer coupling in YBa$_2$Cu$_3$O$_6$.