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

The two-layer square lattice quantum antiferromagnet with spins 1/2 shows a magnetic order-disorder transition at a critical ratio of the interplane t o intraplane couplings. We investigate the dynamics of a single hole in a b ilayer antiferromagnet described by a t-J Hamiltonian To-model the spin bac kground we propose a ground-state wave function for the undoped system that covers both magnetic phases and includes transverse as well as longitudina l spin fluctuations. The photoemission spectrum is calculated using the spi n-polaron picture for the whole range of the ratio of the magnetic coupling s. This allows for the study of the hole dynamics on both sides of the magn etic order-disorder transition. For:small interplane coupling we find a qua siparticle with properties known from the single-layer antiferromagnet, e.g ., the dispersion minimum is at (+/-pi/2, +/-pi/2). For large interplane co upling the hole dispersion is similar to that of a free fermion (with reduc ed bandwidth). The crossover between these two scenarios occurs inside the antiferromagnetic phase, which indicates that the hole dynamics is governed by the local environment of the hole. [S0163-1829(99)04245-9].