Phase transitions and order-by-quantum disorder for the anti- ferromagnetic XY model in the checkerboard lattice

Abstract

In this work we have studied the phases of the XY antiferromagnetic model in the checkerboard lattice (the two-dimensional analog of the pyrochlore lattice). Using the traditional linear spin–wave approximation, we obtain a transition from an order to a disordered phase in some critical value r c = J ′ / J . The phase transition occurs due to quantum fluctuations. However, when we consider higher order perturbations the scenario is entirely different. We have applied the Self-Consistent Harmonic Approximation method and the results show that quantum perturbations induce long-range spin–spin correlations even above the critical point r c . This is a typical feature of order-by-quantum disorder when the system chooses one of the many classical ground states to occupy. We have also determined the thermal phase transitions similar to the Berezinskii–Kosterlitz–Thouless phase transition and the action of a single-ion anisotropy, responsible for a Quantum Phase Transition at zero temperature.