Vortex Structure in Magnetic Nanodots: Dipolar Interaction, Mobile Spin Model, Phase Transition and Melting

Melting in Monolayers : Hexatic and Fluid Phases

There are strong evidences that the melting in two dimensions depends crucially on the form and range of the interaction potentials between particles. We study with Monte Carlo simulations the phase diagram and the melting of a monolayer of point-particles interacting with repulsive Inverse Power Law Interactions, $V(r)=Q^2(σ/r)^n$ where $n$ can take any real positive value ($n$-OCP monolayer). As $n$ is varied from 0 to $\infty$ (Hard Disks), including Coulomb ($n=1$) and Dipolar ($n=3$), melting occurs with different mechanisms and the overall picture permits to understand the diversity of m…

Quantum and thermal melting of stripe forming systems with competing long ranged interactions

We study the quantum melting of stripe phases in models with competing short range and long range interactions decaying with distance as $1/r^σ$ in two space dimensions. At zero temperature we find a two step disordering of the stripe phases with the growth of quantum fluctuations. A quantum critical point separating a phase with long range positional order from a phase with long range orientational order is found when $σ\leq 4/3$, which includes the Coulomb interaction case $σ=1$. For $σ> 4/3$ the transition is first order, which includes the dipolar case $σ=3$. Another quantum critical point…

Metric Features of a Dipolar Model

The lattice spin model, with nearest neighbor ferromagnetic exchange and long range dipolar interaction, is studied by the method of time series for observables based on cluster configurations and associated partitions, such as Shannon entropy, Hamming and Rohlin distances. Previous results based on the two peaks shape of the specific heat, suggested the existence of two possible transitions. By the analysis of the Shannon entropy we are able to prove that the first one is a true phase transition corresponding to a particular melting process of oriented domains, where colored noise is present …

Quantum hexatic order in two-dimensional dipolar and charged fluids

Recent advances in cold atom experimentation suggest that studies of quantum two-dimensional melting of dipolar molecules, with dipoles aligned perpendicular to ordering plane, may be on the horizon. An intriguing aspect of this problem is that two-dimensional \emph{classical} aligned dipoles (already studied in great detail in soft matter experiments on magnetic colloids) are known to melt via a two-stage process, with an intermediate hexatic phase separating the usual crystal and isotropic fluid phases. We estimate here the effect of quantum fluctuations on this hexatic phase, for both dipol…

二维过冷液体中的固有态熔化与玻璃态动力学的起始

Inherent-State Melting and the Onset of Glassy Dynamics in Two-Dimensional Supercooled Liquids

本研究针对二维过冷液体起始温度$T_\ ext{o}$的微观起源不明问题，提出固有态熔化（偶极弹性激发束缚-非束缚转变）是过冷与高温区域的分界，理论结果与多种模型及实验模拟的Mermin-Wagner涨落观测一致。

Solid phases and pairing in a mixture of polar molecules and atoms

We consider a mixture of hard core bosonic polar molecules, interacting via repulsive dipole-dipole interaction, and one atomic bosonic species. The mixture is confined on a two-dimensional square lattice and, at low enough temperatures, can be described by the two-component Bose-Hubbard model. The latter displays a extremely rich phase diagram including solid, superfluid, supersolid phases. Here we mainly focus on the checkerboard molecular solid, stabilized by the long range dipolar interaction, and study how the presence of atoms affects its robustness both at zero and finite temperature. W…

Numerical simulations of two dimensional magnetic domain patterns

I show that a model for the interaction of magnetic domains that includes a short range ferromagnetic and a long range dipolar anti-ferromagnetic interaction reproduces very well many characteristic features of two-dimensional magnetic domain patterns. In particular bubble and stripe phases are obtained, along with polygonal and labyrinthine morphologies. In addition, two puzzling phenomena, namely the so called `memory effect' and the `topological melting' observed experimentally are also qualitatively described. Very similar phenomenology is found in the case in which the model is changed to…

Topological phase diagrams of the frustrated Ising ferromagnet

The emergence of complex modulated structures in the magnetization pattern of thin films is a well-established experimental phenomenology caused by the frustrating effects of competing interactions. Using a coarse-grained version of the Ising ferromagnet with dipolar interactions, we develop a method that uses the information from the microscopic Hamiltonian to predict the specific topological phases present in the temperature-external magnetic field phase diagram. This is done by the combination of mean-field variational calculations and the renormalization group equations from the classical …

图案化二维磁性计算框架

Computational Frameworks for Patterned Two-Dimensional Magnetism

本文综述了图案化二维磁性中的计算框架，涵盖理论模型和数值方法，探讨了几何在控制相稳定性和自旋纹理中的作用。

方格晶格上玻色子的有限温度相和激发：团簇平均场研究

Finite temperature phases and excitations of bosons on a square lattice: A cluster mean field study

本研究采用团簇平均场理论探究方格晶格上硬核与软核玻色子的有限温度相和激发，明确超固体相的热熔化路径与四临界点行为，为超冷原子气体实验提供理论参考。