Kumar Nitin, Gupta Rahul Kumar, Soni Harsh, Ramaswamy Sriram, Sood A K
Department of Physics, Indian Institute of Science, Bangalore 560 012, India.
Tata Institute of Fundamental Research, Gopanpally, Hyderabad 500 107, India.
Phys Rev E. 2019 Mar;99(3-1):032605. doi: 10.1103/PhysRevE.99.032605.
We present an experimental realization of the collective trapping phase transition [Kaiser et al., Phys. Rev. Lett. 108, 268307 (2012)PRLTAO0031-900710.1103/PhysRevLett.108.268307], using motile polar granular rods in the presence of a V-shaped obstacle. We offer a theory of this transition based on the interplay of motility-induced condensation and liquid-crystalline ordering and show that trapping occurs when persistent influx overcomes the collective expulsion of smectic defect structures. In agreement with the theory, our experiments find that a trap fills to the brim when the trap angle θ is below a threshold θ_{c}, while all particles escape for θ>θ_{c}. Our simulations support a further prediction, that θ_{c} goes down with increasing rotational noise. We exploit the sensitivity of trapping to the persistence of directed motion to sort particles based on the statistical properties of their activity.
