8 research outputs found
Coherence of Currents in Mesoscopic Cylinders
The persistent currents driven by the pure Aharonov-Bohm type magnetic field
in mesoscopic normal metal or semiconducting cylinders are studied. A
two-dimensional (2D) Fermi surfaces are characterized by four parameters.
Several conditions for the coherence and enhancement of currents are discussed.
These results are then generalized to a three-dimensional (3D) thin-walled
cylinder to show that under certain geometric conditions on the Fermi surface,
a novel effect - the appearance of spontaneous currents is predicted.Comment: 17 pages, Latex, 8 figures available on request, to be published in
Z.Physik
The Two-fluid Description of a Mesoscopic Cylinder
Quantum coherence of electrons interacting via the magnetostatic coupling and
confined to a mesoscopic cylinder is discussed.
The electromagnetic response of a system is studied. It is shown that the
electromagnetic kernel has finite low frequency limit what implies infinite
conductivity. It means that part of the electrons is in a coherent state and
the system can be in general described by a two-fluid model.
The coherent behavior is determind by the interplay between finite size
effects and the correlations coming from the magnetostatic interactions (the
interaction is considered in the mean field approximation).
The related persistent currents depend on the geometry of the Fermi Surface.
If the Fermi Surface has some flat portions the self-sustaining currents can be
obtained.
The relation of the quantum coherent state in mesoscopic cylinders to other
coherent phenomena is discussed.Comment: 21 pages, Latex, 4 figures, in print in Eur. Phys. J. B (Z. Phys. B
Orbital Magnetic Ordering in Disordered Mesoscopic Systems
We present some model calculations of persistent currents in disordered one-
and two-dimensional mesoscopic systems. We use the tight-binding model and
calculate numerically the currents in small systems for several values of
disorder.
Next we fit appropriate analytical formulae, and using them we find self-
-sustaining currents and critical fields in larger, more realistic systems with
different shapes of the Fermi surfaces.Comment: 16 pages, LaTeX, 8 figures, in print in J. Magn. Magn. Ma
Possibility of long-range order in clean mesoscopic cylinders
A microscopic Hamiltonian of the magnetostatic interaction is discussed. This
long-range interaction can play an important role in mesoscopic systems leading
to an ordered ground state.
The self-consistent mean field approximation of the magnetostatic interaction
is performed to give an effective Hamiltonian from which the spontaneous,
self-sustaining currents can be obtained.
To go beyond the mean field approximation the mean square fluctuation of the
total momentum is calculated and its influence on self-sustaining currents in
mesoscopic cylinders with quasi-1D and quasi-2D conduction is considered. Then,
by the use of the microscopic Hamiltonian of the magnetostatic interaction for
a set of stacked rings, the problem of long-range order is discussed. The
temperature below which the system is in an ordered state is
determined.Comment: 14 pages, REVTeX, 5 figures, in print in Phys. Rev.
Electromagnetic properties of mesoscopic cylinder
The electromagnetic response of a mesoscopic cylinder made of a normal
metal or a semiconductor is studied. The relation between the induced
current J(q, w) and the electric field E(q, w) is derived. It is shown that the
kernel K(q, w) which determines the properties of the system has a finite
limit which implies infinite conductivity. The mesoscopic cylinder by virtue
of its topology and small dimensions can support a persistent current. If the
coherence of currents from different channels is strong enough a novel effect
— the self-sustaining current can be obtained. We show tlat a mesoscopic
multichannel system exhibits some features which bear resemblance to the
superconductor
Persistent currents in carbon nanotubes
Persistent currents driven by a static magnetic flux parallel to the carbon
nanotube axis are investigated. Owing to the hexagonal symmetry of graphene the
Fermi contour expected for a 2D-lattice reduces to two points. However the
electron or hole doping shifts the Fermi energy upwards or downwards and as a
result, the shape of the Fermi surface changes. Such a hole doping leading to
the Fermi level shift of (more or less) 1eV has been recently observed
experimentally. In this paper we show that the shift of the Fermi energy
changes dramatically the persistent currents and discuss the electronic
structure and possible currents for zigzag as well as armchair nanotubes.Comment: 8 text pages, 6 figures, to appear in Physics Letters
Electromagnetic Properties of Mesoscopic Cylinder
The electromagnetic response of a mesoscopic cylinder made of a normal metal or a semiconductor is studied. The relation between the induced current J(q,w) and the electric field E(q,w) is derived. It is shown that the kernel K(q,w) which determines the properties of the system has a finite limit which implies infinite conductivity. The mesoscopic cylinder by virtue of its topology and small dimensions can support a persistent current. If the coherence of currents from different channels is strong enough a novel effect - the self-sustaining current can be obtained. We show that a mesoscopic multichannel system exhibits some features which bear resemblance to the superconductor