2 00 7 Flux - biased mesoscopic rings

Kinetics of magnetic flux in a thin mesoscopic ring biased by a strong external magnetic field is described equivalently by dynamics of a Brownian particle in a tilted wash-board potential. The 'flux velocity', i.e. the averaged time derivative of the total magnetic flux in the ring, is a candidate for a novel characteristics of mesoscopic rings. Its global properties reflect the possibility of accommodating persistent currents in the ring. 1 Mesoscopic rings: two-fluid model Mesoscopic devices have attracted much theoretical and practical attention because they are promising for implementation in ultra-small hybrid elements to test quantum information theory [1]. A large class of such devices is based on ring structures, i.e. the Aharonov-Bohm topology. Such a class contains both superconducting (SQUIDs) and non-superconducting devices. In this paper we study selected kinetic aspects of persistent currents which can be observed in normal metal, semiconducting rings or cylinders and, as probably the most famous examples , in carbon nanotubes or nanotori. We focus our attention on kinetics of magnetic flux in the presence of a strong external static magnetic field. We show that it can be modeled in the same way as the dynamics of a Brownian particle moving in a biased washboard potential. Here, the analog of the position of the Brownian particle is a total magnetic flux. We show that the time derivative of the magnetic flux, i.e. the flux velocity (if we recall the analogy to the dynamics of the Brownian particle) depends strongly on the ability of accommodation of persistent currents by the ring. Persistent currents are equilibrium currents flowing in the Aharonov-Bohm systems which are small enough to preserve phase coherence of electrons [2, 3]. In ideal samples at the vanishing temperature T = 0, all electrons are the carriers of such a current. It is not the case