629 research outputs found
Angular magnetoresistance oscillations in bilayers in tilted magnetic fields
Angular magnetoresistance oscillations (AMRO) were originally discovered in
organic conductors and then found in many other layered metals. It should be
possible to observe AMRO to semiconducting bilayers as well. Here we present an
intuitive geometrical interpretation of AMRO as the Aharonov-Bohm interference
effect, both in real and momentum spaces, for balanced and imbalanced bilayers.
Applications to the experiments with bilayers in tilted magnetic fields in the
metallic state are discussed. We speculate that AMRO may be also observed when
each layer of the bilayer is in the composite-fermion state.Comment: 4 pages, 5 figures, Proceedings of EP2DS-16. V.2: figures corrected,
one reference added. V3: one reference adde
Longitudinal conductivity and transverse charge redistribution in coupled quantum wells subject to in-plane magnetic fields
In double quantum wells electrons experience a Lorentz force oriented
perpendicular to the structure plane when an electric current is driven
perpendicular to the direction of an in-plane magnetic field. Consequently, the
excess charge is accumulated in one of the wells. The polarization of a bilayer
electron system and the corresponding Hall voltage are shown to contribute
substantially to the in-plane conductivity.Comment: 3 pages, 2 figure
A deep photometric survey of the eta Chamaeleontis cluster down to the brown dwarf - planet boundary
We report the outcome of the deep optical/infrared photometric survey of the
central region (33 X 33 arcmin or 0.9 pc^2) of the eta Chamaeleontis pre-main
sequence star cluster. The completeness limits of the photometry are I = 19.1,
J = 18.2 and H = 17.6; faint enough to reveal low mass members down to the
brown dwarf and planet boundary of ~ 13 M_Jup. We found no such low mass
members in this region. Our result combined with a previous shallower (I = 17)
but larger area survey indicates that low mass objects (0.013 < M/M(solar mass)
< 0.075) either were not created in the eta Cha cluster or were lost due to the
early dynamical history of the cluster and ejected to outside the surveyed
areas.Comment: 5 pages with 4 figures, accepted by MNRA
Oscillatory Magneto-Thermopower and Resonant Phonon Drag in a High-Mobility 2D Electron Gas
Experimental and theoretical evidence is presented for new low-magnetic-field
( kG) 1/B-oscillations in the thermoelectric power of a high-mobility
GaAs/AlGaAs two-dimensional (2D) electron gas. The oscillations result from
inter-Landau-Level resonances of acoustic phonons carrying a momentum equal to
twice the Fermi wavenumber at . Numerical calculations show that both 3D
and 2D phonons can contribute to this effect.Comment: 4 pages, 5 figure
Impact of the new solar abundances on the calibration of the PMS binary system RS Cha
Context: In a recent work, we tried to obtain a calibration of the two
components of the pre-main sequence binary system RS Cha by means of
theoretical stellar models. We found that the only way to reproduce the
observational parameters of RS Cha with standard stellar models is to decrease
the initial abundances of carbon and nitrogen derived from the GN93 solar
mixture of heavy elements by a few tenths of dex.
Aims: In this work, we aim to reproduce the observational properties of the
RS Cha stars with stellar evolution models based on the new AGS05 solar mixture
recently derived from a three-dimensional solar model atmosphere. The AGS05
mixture is depleted in carbon, nitrogen and oxygen with respect to the GN93
mixture.
Methods: We calculated new stellar models of the RS Cha components using the
AGS05 mixture and appropriate opacity tables. We sought models that
simultaneously satisfy the observations of the two components (masses, radii,
luminosities, effective temperatures and metallicity).
Results: We find that it is possible to reproduce the observational data of
the RS Cha stars with AGS05 models based on standard input physics. From these
models, the initial helium content of the system is Y~0.255 and its age is
~9.13 +- 0.12 Myr.Comment: Research note accepted in A&A, 5 pages, 2 figure
Quasi two-dimensional carriers in dilute-magnetic-semiconductor quantum wells under in-plane magnetic field
Due to the competition between spatial and magnetic confinement, the density
of states of a quasi two-dimensional system deviates from the ideal step-like
form both quantitatively and qualitatively. We study how this affects the
spin-subband populations and the spin-polarization as functions of the
temperature, , and the in-plane magnetic field, , for narrow to wide
dilute-magnetic-semiconductor quantum wells. We focus on the quantum well
width, the magnitude of the spin-spin exchange interaction, and the sheet
carrier concentration dependence. We look for ranges where the system is
completely spin-polarized. Increasing , the carrier spin-splitting,
, decreases, while increasing , increases.
Moreover, due to the density of states modification, all energetically higher
subbands become gradually depopulated.Comment: 3 pages, 3 figure
Transport in single-molecule transistors: Kondo physics and negative differential resistance
We report two examples of transport phenomena based on sharp features in the
effective density of states of molecular-scale transistors: Kondo physics in
C-based devices, and gate-modulated negative differential resistance
(NDR) in ``control'' devices that we ascribe to adsorbed contamination. We
discuss the need for a statistical approach to device characterization, and the
criteria that must be satisfied to infer that transport is based on single
molecules. We describe apparent Kondo physics in C-based single-molecule
transistors (SMTs), including signatures of molecular vibrations in the Kondo
regime. Finally, we report gate-modulated NDR in devices made without
intentional molecular components, and discuss possible origins of this
property.Comment: 15 pages, 8 figures. To appear in Oct. 2004 issue of Nanotechnology,
proceedings of International Conference on Nanoscale Devices and Systems
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