Projects

2015-2017 COLPHAM
COLlective PHenomena in dense Active Matter: phase transitions and non-equilibrium dynamics.

Marie Skłodowska-Curie Individual Fellowships: Intra-European (MSCA-IF-EF).
Horizon 2020 Framework Programme – European Commission.
Fellow: Demian Levis,  host: Ignacio Pagonabarraga.

Overview: Self-propelled (or active) particles are  units able to convert energy from the environment into directed motion. These can be both living (like bacteria or birds) or artificial (like synthetic Janus colloids or polar grains).  Large assemblies of them constitute the so-called Active Matter, a new kind of dissipative systems driven out-of-equilibrium (by the continuous injection of energy at the level of an individual unit). Active Matter displays a rich non-equilibrium behaviour that strongly differs from traditional equilibrium passive systems. Statistical mechanics can generically describe equilibrium soft matter systems made of interacting particles,  however, active matter evolves in a non-equilibrium manner, thus demanding a new conceptual framework to describe it. By combining numerical simulations and theoretical analysis of model systems, we aim to elucidate the general principles governing the physics of many-body systems of active particles when excluded-volume interactions compete with internal driving forces,  and give an answer to the following question: How are the structure of the liquid and solid phases, and their mechanical response to an applied deformation, affected by self-propulsion? The completion of this research project will represent a major contribution into this fast-growing field with direct applications in materials science and biophysics.

Phase separation purely driven by self-propulsion in a system of Active Brownian Hard Disks at 12% packing fraction with open boundaries (left) and confined between two hard walls (right).
Pattern formation induced by rotations in Chiral Active Particles.
Synchronization of Self-Propelled Hard Disks carrying an internal phase oscillator. The color code represents the internal phase of each particle.

References

Active Brownian Equation of State: Metastability and Phase Coexistence
Demian Levis, Joan Codina and Ignacio Pagonabarraga
Soft Matter 13, 8113 (2017); arXiv

Collective behaviour of Chiral Active Matter: Pattern Formation and Enhanced Flocking
Benno Liebchen* and Demian Levis*
Phys. Rev. Lett. 119, 058002 (2017); arXiv * Equal contribution
c.f. press release (in English, Spanish and Catalan) UB news

Synchronization in dynamical networks of locally coupled self-propelled oscillators
Demian Levis, Ignacio Pagonabarraga and Albert Diaz-Guilera
Phys. Rev. X 7, 011028 (2017) ;  arXiv
c.f. press release (in Spanish) Revista Española de Física 31, 3 (2017)