Frustrated Ising model on the honeycomb lattice: Metastability and universality

We study the Ising model with competing ferromagnetic nearest- and antiferromagnetic next-nearest-neighbor interactions of strengths J 1 > 0 and J 2 < 0 , respectively, on the honeycomb lattice. For J 2 > − J 1 / 4 it has a ferromagnetic ground state, and previous work has shown that at least for J 2 ≳ − 0.2 J 1 the transition is in the Ising universality class. For even lower J 2 some indicators pointing towards a first-order transition were reported. By utilizing population annealing Monte Carlo simulations together with a rejection-free and adaptive update, we can equilibrate systems with J 2 as low as − 0.23 J 1 . By means of a finite-size scaling analysis we show that the system undergoes a second-order phase transition within the Ising universality class at least down to J 2 = − 0.23 J 1 and, most likely, for all J 2 > − J 1 / 4 . As we show here, there exist very long-lived metastable states in this system explaining the first-order like behavior seen in only partially equilibrated systems.