Time Reversal Symmetry Breaking and Directed Assembly of Active Colloids

Mike Cates (Cambridge)

Active colloids are self-propelled particles whose microscopic dynamics breaks time-reversal symmetry (TRS) by continuously consuming fuel. Some aspects of their behaviour can be described by simple scalar field theories, such as phi-4 theory, with minimal TRS-breaking terms. TRS violation can be combined with broken spatial reflection symmetry to create ratchets and hence globally circulating currents. In some systems, the self-propulsion speed can be controlled with a light intensity field. I will explore how this might, in principle, allow one to create ratchets and other microfluidic devices from a primordial soup of active colloids purely by light intensity modulation. Finally I will discuss strategies for quantifying whether, under given conditions, microscopic TRS violation survives coarse-graining to remain relevant to large-scale system behaviour.