Doped bilayer antiferromagnets: Hole dynamics on both sides of a magnetic ordering transition

TL;DR

This paper studies how a single hole moves in a bilayer antiferromagnet across a magnetic transition, revealing a crossover from quasiparticle to free-fermion behavior influenced by the local environment.

Contribution

It introduces a ground-state wave function covering both magnetic phases and calculates the photoemission spectrum across the transition using a spin-polaron approach.

Findings

Quasiparticle behavior in weak interlayer coupling resembles single-layer antiferromagnet.

Strong interlayer coupling leads to hole dispersion similar to free fermions.

The crossover occurs within the antiferromagnetic phase, driven by local environment effects.

Abstract

The two-layer square lattice quantum antiferromagnet with spins 1/2 shows a magnetic order-disorder transition at a critical ratio of the interplane to intraplane couplings. We investigate the dynamics of a single hole in a bilayer antiferromagnet described by a t-J Hamiltonian. To model the spin background we propose a ground-state wave function for the undoped system which covers both magnetic phases and includes transverse as well as longitudinal spin fluctuations. The photoemission spectrum is calculated using the spin-polaron picture for the whole range of the ratio of the magnetic couplings. This allows for the study of the hole dynamics of both sides of the magnetic order-disorder transition. For small interplane coupling we find a quasiparticle with properties known from the single-layer antiferromagnet, e.g., the dispersion minimum is at (pi/2,pi/2). For large interplane coupling the hole dispersion is similar to that of a free fermion (with reduced bandwidth). The cross-over between these two scenarios occurs inside the antiferromagnetic phase which indicates that the hole dynamics is governed by the local environment of the hole.