טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentItamar Shamai
SubjectDefect-Mediated Melting in Antiferromagnetic Systems
DepartmentDepartment of Physics
Supervisor Professor Podolsky Daniel
Full Thesis textFull thesis text - English Version


Abstract

The mechanism of melting, the process of a solid becoming a liquid, is a central and ongoing subject of research in condensed matter physics. In three dimensions, melting is believed to always be a first-order transition. In two dimensions, there is an additional possibility, and melting can occur through a pair of continuous transitions mediated by unbinding of topological defects. In this thesis, we incorporate the phenomenon of antiferromagnetism to the theory of two dimensional melting, and study the melting process of a two-dimensional XY antiferromagnet.

It can easily be seen that magnetic ordering in an antiferromagnet is highly affected by the underlying lattice structure. This gives an interesting interplay between magnetic and lattice ordering. Many fundamental questions then emerge: How is the interplay between lattice and magnetism modeled? What are the theoretically possible phases of such a material? What is the nature of transitions between these phases?

We attack the problem using a Coulomb gas representation that enables us to treat lattice and magnetism on the same footing and to encode the interaction between them easily. Using the renormalization group, we build rich phase diagrams both for a two-dimensional XY antiferromagnet and for a closely related system that can be realized experimentally. We find novel phases, among them a hexatic antiferromagnet and a liquid antiferromagnet.