Order by disorder induce dimer crystal in the frustrated honeycomb bilayer

F. A. GÓMEZ ALBARRACÍN; H. D. ROSALES

Congreso; VI Reunión Nacional de Sólidos 2015; 2015

Frustration has proved to give rise to an extremely rich phenomenology in both quantum and classical systems. The inclusion of an external magnetic field could change the degeneracy and topology of the ground state manifold stabilizing different ground states. In this work we present a detailed study of the antiferromagnetic classical Heisenberg model on a bilayer honeycomb lattice in a highly frustrated regime in presence of a magnetic field. This study shows strong evidence of entropic order-bydisorder selection in different sectors of the magnetization curve. For antiferromagnetic couplings J1 = Jx = Jp/3, we find that at low temperatures there are two different regions in the magnetization curve selected by this mechanism with different number of soft and zero modes. These regions are separated by a classical pseudoplateau at M = 1/2, which is not fully collinear. In fact, it can be described as a collinear dimer and a "classical singlet". Both regions at low temperature break Z2 symmetry, and split the system in sublattices of spin pairs ("classical dimers"). We present the order parameter and binder cumulant calculations to show the Z2 symmetry breaking. Using the specific heat, we present the T vs h phase diagram. At higher temperatures, there is a crossover from the conventional paramagnet to a cooperative magnet. As the temperature is lowered, the order by disorder mechanism is at play, and the differentsymmetry breaking phases arise.