Mesoscopic rings : two - fluid model

Kinetics of magnetic flux in the thin mesoscopic ring biased by an external magnetic flux exhibits the ratchet-like behavior. The 'flux velocity', i.e. the averaged time derivative of magnetic flux produced by 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 attract much theoretical and practical attention as they can serve as a stage for testing quantum information theory [1]. The large class of such devices is based on a ring, i.e. 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 known to flow in normal metal and semiconducting rings or cylinders with carbon nanotubes or nanotori as a famous examples. We focus our attention on the kinetics of magnetic flux in the presence of large external magnetic bias assumed to be static. As a result we obtain an effective Brownian particle in a ratchet-like potential. The analog of the 'position' is here a magnetic flux. We show that the time derivative of magnetic flux i.e., using the 'Brownian particle' analogy, the velocity depends strongly on the ability of accommodation persistent currents by the ring. Persistent currents are equilibrium currents flowing in Aharonov-Bohm systems small enough to preserve phase coherence of electrons [2, 3]. In ideal samples at vanishing temperature T = 0 all electrons are carriers of such a current. It is not the case in non-zero temperatures T > 0 where some of electrons are no longer coherent and are the source of the 'normal' ohmic current. Let us consider now a mesoscopic ring placed in a uniform magnetic