Phase transitions in classical spin models with continuous rotational symmetry

by Prof. Alessandro Giuliani (Università Roma Tre)

Monday 7 Feb 2022, 15:00 → Tuesday 8 Feb 2022, 11:00 Europe/Rome

Abstract

In this 4-hours mini-course, I will provide an introduction to the theory of phase transitions in classical spin models with continuous rotational symmetry, such as the XY (or rotator) model and the Heisenberg model. I will discuss the predictions on the phase diagram of these models based on the Gaussian approximation, also known as "spin wave theory". I will state and sketch the proofs of two theorems substantiating the expected picture, namely:

• the Mermin-Wagner theorem, on the absence of long range orientational order in one or two dimensions;
   
• the Frohlich-Simon-Spencer theorem, on the existence of long range  orientational order in three or more dimensions.

 

Schedule: the mini course will be held onsite at GSSI (room D) and streamed on zoom, according to the following schedule:

February 7th:   15-17
February 8th:     9-11

People interested in the onsite or online participation may contact Serena Cenatiempo for further information (serena.cenatiempo@gssi.it).