Condensed Matter Theory

Abstract:

Individually propulsive catalytic Janus particle swimmers are observed to self-assemble into aggregate swimmers with a wide variety of translational and rotational velocities. The trajectory for a given doublet is shown to be determined by the frozen in relative orientation of the particles. The new swimmers suggest applications as transport and mixing devices, and will allow study of the interplay between propulsion and Brownian phenomena. Furthermore this random assembly process can be controlled using external magnetic fields to orientate individual ferromagnetic swimming particles so as to favor the production of swimmers with particular desirable configurations resulting in linear trajectories. This approach also produces swimmers that can be orientated, and so "steered" by external fields. © 2011 Materials Research Society.

Abstract:

We studied charged excitations of the ν=5/2 fractional quantum Hall state allowing for spin depolarization. It is generally accepted that the ground state is a spin-polarized incompressible quantum liquid, adiabatically connected to the Pfaffian state, whose spin-polarized quasiholes (QHs) obey non-Abelian statistics. Using numerical diagonalization and taking account of non-zero well widths we demonstrated that at a sufficiently low Zeeman energy it is energetically favorable for pairs of charge e/4 QHs to bind into charge e/2 Skyrmions. We showed that Skyrmion formation is further promoted by disorder, and argue that this can lead to a depolarized ground state in realistic experimental situations. © 2011 American Institute of Physics.

Abstract:

We discuss the unusual critical behavior of a generalized XY model containing both 2π-periodic and π-periodic couplings between sites, allowing for ordinary vortices and half-vortices. The phase diagram of this system includes both single-particle condensate and pair-condensate phases. Using a field theoretic formulation and worm algorithm Monte Carlo simulations, we show that in two dimensions it is possible for the system to pass directly from the disordered (high temperature) phase to the single particle (quasi)condensate via an Ising transition, a situation reminiscent of the "deconfined criticality" scenario.

Abstract:

Single file translocation of a homopolymer through an active channel under the presence of a driving force is studied using Langevin dynamics simulation. It is shown that a channel with sticky walls and oscillating width could lead to significantly more efficient translocation as compared to a static channel that has a width equal to the mean width of the oscillating pore. The gain in translocation exhibits a strong dependence on the stickiness of the pore, which could allow the polymer translocation process to be highly selective.