XY behaviour of the 2D S=1/2 antiferromagnet in a field

The S=1/2 quantum Heisenberg antiferromagnet on the square lattice in a uniform arbitrary magnetic field is studied by means of quantum Monte Carlo simulations. The applied field induces an effective easy-plane anisotropy and consequently a Berezhinskii–Kosterlitz–Thouless (BKT) transition: the expected BKT behaviour is observed to persist both in the limit of vanishing field and near the saturation field. Experimental implications are discussed.