Physik-Preis Dresden 2025: Unified theory of interacting Dirac fermions in two dimensions

Datum

18.11.2025

Zeit

16:00 - 18:30

Sprecher

Prof. Dr. Igor Herbut

Zugehörigkeit

Simon Fraser University

Sprache

en

Hauptthema

Physik

Andere Themen

Physik

Beschreibung

Dirac fermions appear as low-energy quasiparticle excitations in many condensed matter systems of current interest. They are often weakly interacting, as famously in graphene, for example, but at interactions of intermediate strength they can also exhibit many ordered ground states by going through phase transitions at which gapless Dirac fermions play a crucial role. Prime example of such a transition occurs in the Hubbard model on honeycomb lattice at half filling, which has a Dirac semimetal - Mott insulator transition in the so-called Heisenberg-Gross-Neveu universality class. I will present a unified theory of order parameters for Dirac systems in two-dimensions, based on hidden O(8) symmetry that emerges in the Majorana representation of Dirac fermions. The interacting relativistic field theory with the full O(8) symmetry turns out to be nothing else but the celebrated Gross-Neveu model. I will argue, however, that this well-studied model has a novel phase transition at a strong interaction of previously poorly unexplored sign, at which the O(8) becomes spontaneously broken. The problem of the universality class of this transition, in which the order parameter is a symmetric second-rank tensor coupled to relativistic fermions, and the effect of a finite chemical potential on the phase diagram, will be also discussed.

Letztmalig verändert: 03.10.2025, 07:39:26