In a newly published Emerging Talents paper in Journal of Physics A: Mathematical and Theoretical Alexandre Lazarescu investigates a Generic dynamical phase transition in onedimensional bulkdriven lattice gases with exclusion. Alexandre spoke to JPhys+ to explain more about dynamical phase transitions.
An isolated system of particles hopping on a lattice and interacting together is known to have large scale dynamics which follow a hydrodynamic equation, where the evolution of the local average density of particles satisfies a continuity equation , involving noisy currents whose distribution only depend on , and not on any higher moment of the particle distribution. This happens when the spatial correlations present at the microscopic scale disappear at the macroscopic scale, making the system much simpler to analyse.
One such system, named the totally asymmetric simple exclusion process (TASEP – figure 1), is particularly interesting in that context: it is hydrodynamic as long as the current of particles fluctuates below a certain threshold, but longrange spatial correlations appear when it goes above it, through a socalled `dynamical phase transition’. Figure 2(a) shows the dynamical phase diagram of the TASEP in terms of the two boundary rates and the fluctuation of the current with respect to the typical current . That transition can be seen in the scaling of the probability to observe a certain current: it is extensive in the system size in the correlated phase, and is independent of in the hydrodynamic phase.
The TASEP happens to be exactly solvable, which is a blessing and a curse: we can perform a very precise analysis of said phase transition, but the methods involved are not transposable to other models. In spite of that, I was able to use nonspecific methods to analyse extreme fluctuations of a large class of nonsolvable generalisations of the TASEP, with arbitrary sitedependent jump rates and extra interactions. I found that the scalings of the probabilities of very low and very high currents are the same as for the regular TASEP, and I conjecture that a similar dynamical phase transition separates those behaviours. This phase transition can be understood by looking at the typical current for a given density, (figure 2(b), black curve). Because of the exclusion condition, the current vanishes at and , implying that it has a maximal value somewhere inbetween. The system can change its density by maintaining a localised defect, at a nonextensive probability cost, but the accessible currents are then all below (blue line). The only way for the system to obtain larger currents (red line) is by producing spatial correlations, the cost of which is extensive. The next step would be to find ways to get more precise information on the nature of the transition.
About the Author
Alexandre Lazarescu is a postdoctoral researcher in the Complex Systems and Statistical Mechanics group at the University of Luxembourg, led by Prof. Massimiliano Esposito. He was previously at the Institute for Theoretical Physics at KU Leuven, after completing a PhD at the Institut de Physique Théorique at CEA Saclay.
Read More:

 Journal of Physics A: Mathematical and Theoretical: Emerging Talents Special Issue
 Generic dynamical phase transition in onedimensional bulkdriven lattice gases with exclusion
 Bell scenarios with communication: an Emerging Talents Lab Talk with Jonatan Brask
 Topical Review: The physicist’s companion to current fluctuations: onedimensional bulkdriven lattice gases
 An exact formula for the statistics of the current in the TASEP with open boundaries
This work is licensed under a Creative Commons Attribution 3.0 Unported License.
Author image owned by Alexandre Lazarescu, used with permission. Figure 1 and Figure 2 from Alexandre Lazarescu 2017 J. Phys. A: Math. Theor. 50 254004 © 2017 IOP Publishing Ltd.
Categories: Journal of Physics A: Mathematical and Theoretical