Ground state properties and dynamics of the bilayer t-J model

TL;DR

This study uses exact diagonalization to explore how bilayer t-J models transition from 3D antiferromagnetic correlations to inter-layer singlet states as the inter-layer exchange ratio increases, revealing a crossover at J_perp/J around 0.2.

Contribution

It provides detailed insights into the ground state properties and the crossover behavior of the bilayer t-J model, highlighting the impact of inter-layer coupling on magnetic and pairing correlations.

Findings

Crossover from 3D antiferromagnetic correlations to inter-layer singlets.

Persistence of intra-layer d_(x2-y2) hole pairs at small J_perp/J.

Large J_perp/J leads to s-like symmetry ground state and suppressed intra-layer correlations.

Abstract

We present an exact diagonalization study of bilayer clusters of t-J model. Our results indicate a crossover between two markedly different regimes which occurs when the ratio J_perp/J between inter-layer and intra-layer exchange constants increases: for small J_perp/J the data suggest the development of 3D antiferromagnetic correlations without appreciable degradation of the intra-layer spin order and the d_(x2-y2) hole pairs within the planes persist. For larger values of J_perp/J local singlets along the inter-layer bonds dominate, leading to an almost complete suppression of the intra-layer spin correlation and the breaking of the intra-layer pairs. The ground state with two holes in this regime has s-like symmetry. The data suggest that the crossover may occur for values of J_perp/J as small as 0.2. We present data for static spin correlations, spin gap, and electron momentum distribution and spectral function of the `inter-layer RVB state' realized for large J_perp/J. The latter deviates from the single layer ground state, making it an implausible candidate for modelling high-temperature superconductors.