1,323 research outputs found
Coulomb correlations and coherent charge tunneling in mesoscopic coupled rings
We study the effect of a strong electron-electron (e-e) interaction in a
system of two concentric one-dimensional rings with incommensurate areas A_1
and A_2, coupled by a tunnel amplitude. For noninteracting particles the
magnetic moment (persistent current) m of the many-body ground state and first
excited states is an irregular function of the external magnetic field. In
contrast, we show that when strong e-e interactions are present the magnetic
field dependence of m becomes periodic. In such a strongly correlated system
disorder can only be caused by inter-ring charge fluctuations, controllable by
a gate voltage. The oscillation period of m is proportional to 1/(A_1 + A_2) if
fluctuations are suppressed. Coherent inter-ring tunneling doubles the period
when charge fluctuations are allowed.Comment: 4 pages, 4 eps figure
The ALTO project at IPN Orsay
In order to probe neutron rich radioactive noble gases produced by
photo-fission, a PARRNe1 experiment (Production d'Atomes Radioactifs Riches en
Neutrons) has been carried out at CERN. The incident electron beam of 50 MeV
was delivered by the LIL machine: LEP Injector Linac. The experiment allowed to
compare under the same conditions two production methods of radioactive noble
gases: fission induced by fast neutrons and photo-fission. The obtained results
show that the use of the electrons is a promising mode to get intense neutron
rich ion beams. Thereafter, the success of this photo-fission experiment, a
conceptual design for the installation at IPN Orsay of a 50 MeV electron
accelerator close to the PARRNe-2 device has been worked out: ALTO Project.
This work has started within a collaboration between IPNO, LAL and CERN groups.Comment: 14 pages, pdf file, International School-Seminar on Heavy-Ion Physics
7 (2002
Spin-dependent thermoelectric transport coefficients in near-perfect quantum wires
Thermoelectric transport coefficients are determined for semiconductor
quantum wires with weak thickness fluctuations. Such systems exhibit anomalies
in conductance near 1/4 and 3/4 of 2e^2/h on the rising edge to the first
conductance plateau, explained by singlet and triplet resonances of conducting
electrons with a single weakly bound electron in the wire [T. Rejec, A. Ramsak,
and J.H. Jefferson, Phys. Rev. B 62, 12985 (2000)]. We extend this work to
study the Seebeck thermopower coefficient and linear thermal conductance within
the framework of the Landauer-Buettiker formalism, which also exhibit anomalous
structures. These features are generic and robust, surviving to temperatures of
a few degrees. It is shown quantitatively how at elevated temperatures thermal
conductance progressively deviates from the Wiedemann-Franz law.Comment: To appear in Phys. Rev. B 2002; 3 figure
Giant lasing effect in magnetic nanoconductors
We propose a new principle for a compact solid-state laser in the 1-100 THz
regime. This is a frequency range where attempts to fabricate small size lasers
up till now have met severe technical problems. The proposed laser is based on
a new mechanism for creating spin-flip processes in ferromagnetic conductors.
The mechanism is due to the interaction of light with conduction electrons; the
interaction strength, being proportional to the large exchange energy, exceeds
the Zeeman interaction by orders of magnitude. On the basis of this
interaction, a giant lasing effect is predicted in a system where a population
inversion has been created by tunneling injection of spin-polarized electrons
from one ferromagnetic conductor to another -- the magnetization of the two
ferromagnets having different orientations. Using experimental data for
ferromagnetic manganese perovskites with nearly 100% spin polarization we show
the laser frequency to be in the range 1-100 THz. The optical gain is estimated
to be of order 10^7 cm^{-1}, which exceeds the gain of conventional
semiconductor lasers by 3 or 4 orders of magnitude. A relevant experimental
study is proposed and discussed.Comment: 4 pages, 3 figure
Electromechanics of charge shuttling in dissipative nanostructures
We investigate the current-voltage (IV) characteristics of a model
single-electron transistor where mechanical motion, subject to strong
dissipation, of a small metallic grain is possible. The system is studied both
by using Monte Carlo simulations and by using an analytical approach. We show
that electromechanical coupling results in a highly nonlinear IV-curve. For
voltages above the Coulomb blockade threshold, two distinct regimes of charge
transfer occur: At low voltages the system behave as a static asymmetric double
junction and tunneling is the dominating charge transfer mechanism. At higher
voltages an abrupt transition to a new shuttle regime appears, where the grain
performs an oscillatory motion back and forth between the leads. In this regime
the current is mainly mediated by charges that are carried on the grain as it
moves from one lead to the other.Comment: 8 pages, 10 figures, final version to be published in PR
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