Active matter

General introduction

One basic ingredient of life is directed motion found across all scales from molecular motors marching along microtubules, suspensions of bacteria, to flocks of birds. To this end, free energy supplied by some means has to be converted, which drives life out of thermal equilibrium. Even in simple and artificial systems, the combination of directed motion with interactions between many similar "units" leads to fascinating collective behavior and dynamical patterns.

Active Brownian particles

Following a statistical physics perspective, we focus on a minimal model that combines directed motion with volume exclusion.


  • Negative Interfacial Tension in Phase-Separated Active Brownian Particles
    J. Bialké, J.T. Siebert, H. Löwen, and T. Speck
    Phys. Rev. Lett. 115, 098301 (2015)
    abstract preprint
  • Dynamical mean-field theory and weakly non-linear analysis for the phase separation of active Brownian particles
    T. Speck, A.M. Menzel, J. Bialké, and H. Löwen
    J. Chem. Phys. 142, 224109 (2015)
    abstract preprint
  • Active colloidal suspensions: Clustering and phase behavior
    J. Bialké, T. Speck, and H. Löwen
    J. Non-Cryst. Solids 407, 367 (2015)
    abstract preprint
  • Effective Cahn-Hilliard Equation for the Phase Separation of Active Brownian Particles
    T. Speck, J. Bialké, A.M. Menzel, and H. Löwen
    Phys. Rev. Lett. 112, 218304 (2014)
    abstract preprint
  • Dynamical Clustering and Phase Separation in Suspensions of Self-Propelled Colloidal Particles
    I. Buttinoni, J. Bialké, F. Kümmel, H. Löwen, C. Bechinger, and T. Speck
    Phys. Rev. Lett. 110, 238301 (2013)
    abstract preprint

Quorum sensing

am-quorumBesides physical interactions, some microorganisms can react to their environment through sensing certain signaling molecules emitted by other members of a population. This is a simple form of communication, in which a population follows a predefined action once a quorum has formed. One example is V. fischeri, which controls bioluminescence in accordance with its population density. We are studying how collective behavior and pattern formation can arise in simple models combining directed motion with motility changes triggered by the local concentration of signaling molecules.


  • Collective Behavior of Quorum-Sensing Run-and-Tumble Particles under Confinement
    M. Rein, N. Heinß, F. Schmid, and T. Speck
    Phys. Rev. Lett. 116, 058102 (2016)
    abstract preprint