Kinked Entropy and Discontinuous Microcanonical Spontaneous Symmetry Breaking
Abstract
Spontaneous symmetry breaking (SSB) in statistical physics is a macroscopic collective phenomenon. For the paradigmatic Q state Potts model it means a transition from the disordered colorsymmetric phase to an ordered phase in which one color dominates. Existing mean field theories imply that SSB in the microcanonical statistical ensemble (with energy being the control parameter) should be a continuous process. Here we study microcanonical SSB on the randomgraph Potts model and discover that the entropy is a kinked function of energy. This kink leads to a discontinuous phase transition at certain energy density value, characterized by a jump in the density of the dominant color and a jump in the microcanonical temperature. This discontinuous SSB in random graphs is confirmed by microcanonical Monte Carlo simulations, and it is also observed in bonddiluted finitesize lattice systems.
 Publication:

Physical Review Letters
 Pub Date:
 April 2019
 DOI:
 10.1103/PhysRevLett.122.160601
 arXiv:
 arXiv:1901.00125
 Bibcode:
 2019PhRvL.122p0601Z
 Keywords:

 Condensed Matter  Statistical Mechanics
 EPrint:
 16 pages, extensively revised and improved