Non-Markovian Effects on the Brownian Motion of a Free Particle

Non-Markovian effects upon the Brownian movement of a free particle in the presence as well as in the absence of inertial force are investigated within the framework of Fokker-Planck equations (Rayleigh and Smoluchowski equations). More specifically, it is predicted that non-Markovian features can enhance the values of the mean square displacement and momentum, thereby assuring the mathematical property of differentiability of the these physically observable quantities

Anti-Social Realism

Work included in a group exhibition at Charlie Smith Gallery, London curated by Juan Bolivar and John Stark. Exhibting artists include: Juan Bolivar, Dan Coombs, Graham Crowley, Karen David, Nathan Eastwood, Geraint Evans, John Greenwood, Sigrid Holmwood, Kate Lyddon, Maharishi x Rebecca & Mike, John Salt, John Stark. The term 'Anti-Social Realism', which acts as this exhibitions title, is not one that is commonly understood. It is intended to pose questions such as: is 'revolutionary' art a viable possibility today? What does it mean to be (anti) social in an increasingly interconnected but physically separated society? Can we, through archaic practices such as painting and sculpture, engage with notions of 'social realism’ now presented on a daily basis through the new silver-screen veneer of the digital age? In response, this exhibition attempts to pose pictorial possibilities and create tensions through the selected artworks, tackling notions of contemporary realism and in turn offering us a distant echo of a political reality. The wry misnomer of the exhibition title slips between many interwoven threads, simultaneously conjuring up images of 'anti-social behaviour orders' (ASBO), anarchist riots, or the solitary artist locked away from the world attempting to connect on a higher level. In this light, the exhibiting artists are presented as 'social mystics' and it could be said that their work operates by a means of turning inwards to create social radiation

Persistent charge and spin currents in the long wavelength regime for graphene rings

We address the problem of persistent charge and spin currents on a Corbino disk built from a graphene sheet. We consistently derive the Hamiltonian including kinetic, intrinsic (ISO) and Rashba spin-orbit interactions in cylindrical coordinates. The Hamiltonian is carefully considered to reflect hermiticity and covariance. We compute the energy spectrum and the corresponding eigenfunctions separately for the intrinsic and Rashba spin-orbit interactions. In order to determine the charge persistent currents we use the spectrum equilibrium linear response definition. We also determine the spin and pseudo spin polarizations associated with such equilibrium currents. For the intrinsic case one can also compute the correct currents by applying the bare velocity operator to the ISO wavefunctions or alternatively the ISO group velocity operator to the free wavefunctions. Charge currents for both SO couplings are maximal in the vicinity of half integer flux quanta. Such maximal currents are protected from thermal effects because contributing levels plunge ($\sim$1K) into the Fermi sea at half integer flux values. Such a mechanism, makes them observable at readily accessible temperatures. Spin currents only arise for the Rashba coupling, due to the spin symmetry of the ISO spectrum. For the Rashba coupling, spin currents are cancelled at half integer fluxes but they remain finite in the vicinity, and the same scenario above protects spin currents

Gauge field theory approach to spin transport in a 2D electron gas

We discuss the Pauli Hamiltonian including the spin-orbit interaction within an U(1) x SU(2) gauge theory interpretation, where the gauge symmetry appears to be broken. This interpretation offers new insight into the problem of spin currents in the condensed matter environment, and can be extended to Rashba and Dresselhaus spin-orbit interactions. We present a few outcomes of the present formulation: i) it automatically leads to zero spin conductivity, in contrast to predictions of Gauge symmetric treatments, ii) a topological quantization condition leading to voltage quantization follows, and iii) spin interferometers can be conceived in which, starting from a arbitrary incoming unpolarized spinor, it is always possible to construct a perfect spin filtering condition.Comment: Invited contribution to Statphys conference, June 2009, Lviv (Ukraine

How to prepare quantum states that follow classical paths

We present an alternative quantization procedure for the one-dimensional non-relativistic quantum mechanics. We show that, for the case of a free particle and a particle in a box, the complete classical and quantum correspondence can be obtained using this formulation. The resulting wave packets do not disperse and strongly peak on the classical paths. Moreover, for the case of the free particle, they satisfy minimum uncertainty relation.Comment: 10 pages, 3 figures, to appear in Europhysics Letter