Suropriya Saha

Max Planck Institute, Goettingen

I, Suropriya Saha, obtained my PhD from Institute of Science Bangalore in 2014. During my PhD, I worked on the collective dynamics of phoretically driven matter, focussing mainly on Janus colloids. I did my first postdoc in MPIPKS Dresden working on the rheological properties of protein droplets. After my stint in Dresden, I joined the group living matter physics in MPIDS Goettingen as a postdoc. Since March of this year I am a group leader in the department with my group 'Field theories of active matter'. My current research interests are in non-reciprocally interacting matter, with a focus on systems with number conservations. In my group we are exploring the pattern forming abilities and diversity of this new class of active matter.


Tuesday April 18th

Scalar active mixtures: the non-reciprocal Cahn-Hilliard model

Pair interactions between active particles need not follow Newton’s third law. In this work, we propose a continuum model of pattern formation due to nonreciprocal interaction between multiple species of scalar active matter. The classical Cahn-Hilliard model is minimally modified by supplementing the equilibrium Ginzburg-Landau dynamics with particle-number-conserving currents, which cannot be derived from a free energy, reflecting the microscopic departure from action-reaction symmetry. The strength of the asymmetry in the interaction determines whether the steady state exhibits a macroscopic phase separation or a traveling density wave displaying global polar order. The latter, which is equivalent to an active self-propelled smectic phase, coarsens via annihilation of defects, whereas the former structure undergoes Ostwald ripening. The emergence of traveling density waves, which is a clear signature of broken time-reversal symmetry in this active system, is a generic feature of any multicomponent mixture with microscopic nonreciprocal interactions. Further, we explore the notion of nonlinear non-reciprocity and consider a model in which the nonreciprocal interactions depend on the local values of the scalar fields. For generic cases where such couplings exist, we observe the emergence of spatiotemporal chaos in the steady-state associated with a local restoration of PT symmetry in fluctuating spatial domains.