Possible splitting of a phase transition in a 2D XY model

Snehadri Bihari Ota, Smita Ota

J. Szṅajd, J. Zittartz

Nguyễn Thị Minh Huyền, Lưu Bích Linh, Bui Thi Toan Thu +5 more

In this work the results of the study on a generalization of the XY model with an additional q-fold nematic-like term through Monte Carlo simulations in two dimensions (2D) have been presented. While the conventional 2D XY model has only integer vortexes, the generalized 2D XY model has both integer and non-integer 1/q vortexes, making the phase diagram of the generalized 2D XY model is much richer than that of the conventional 2D XY model. Here, we located the phase transition between the disordered phase (P), the quasi-long-range order phase (F), and the nematic phase (N) for the case of q = 3. We provided the numerical evidence to clarify the N−F phase transition of either the first-ordered or second-ordered phase transition. The results showed that the N−F phase transition is the second-ordered, not the first-order phase transition.

Jae-Kwon Kim

Pascal Simon

We consider the 2D J 1 − J 2 classical XY model on a square lattice. In the frustrated phase corresponding to J 2 > J 1 /2, an Ising order parameter emerges by an "order due to disorder" effect. This leads to a discrete symmetry plus the O (2) global one. We formulate the problem in a Coulomb gas language and show by a renormalization group analysis that only two phases are still possible: a locked phase at low temperature and a disordered one at high temperature. The transition is characterized by the loss of Ising and XY order at the same point. This analysis suggests that the 2D J 1 − J 2 XY model is in the same universality class as XY-Ising models.

Antonio S. T. Pires