Evidence of Kosterlitz-Thouless phase transitions in the Ising model with dipolar interactions

作     者：M. A. Bab G. P. Saracco 

作者机构：Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA) UNLP CCT La Plata-CONICET c.c. 16 Suc. 4 (1900)La Plata Argentina 

出 版 物：《Physical Review E》 (物理学评论E辑：统计、非线性和软体物理学)

年 卷 期：2019年第100卷第2期

页      面：022143-022143页

核心收录：

学科分类：07[理学] 070203[理学-原子与分子物理] 0702[理学-物理学] 

基　　金：CONICET, Argentina [PIP0524] UNLP, Argentina [X11/784] 

主　　题：Critical phenomena Magnetic phase transitions Nematic phase transition Phase diagrams Phase transitions Lattice models in statistical physics Thin films Metropolis algorithm Monte Carlo methods 

摘      要：The ferromagnetic bidimensional Ising model with dipolar interactions has been proposed to model ultrathin films with strong out-of-plane anisotropy. The phase diagram presents a rich phenomenology that includes low-temperature phases characterized by stripes of width n (hn) and a high-temperature phase with domains of stripes with mutually perpendicular orientations, named tetragonal liquid (TL). The latter phase can be reached by two possible ways. One of them is the direct transition hn to TL, and the other one is through an intermediate phase with orientational order but short-range positional disorder, named nematic phase (NM). The regions of the phase diagram where these transitions occur, as well as their character, remain an open question and are the object of the present work. In order to clarify this topic, intensive Monte Carlo simulations were performed by employing short-time dynamics as the main tool for studying the phase transition behavior. The dynamic evolution of the orientational order parameter and its moments are measured for selected values of the ratio between the ferromagnetic exchange and dipolar constants, called δ. The obtained results indicate that the intermediate NM phase is present for δ≥2 in narrow ranges of temperatures. Also, the results suggest that both transitions, i.e., hn-NM and NM-TL, have a Kosterlitz-Thouless character. This type of topological transition is observed in continuous bidimensional models and have been proposed for discrete ones, as in the case of the present work.