117 research outputs found
Weak antilocalization in quantum wells in tilted magnetic fields
Weak antilocalization is studied in an InGaAs quantum well. Anomalous
magnetoresistance is measured and described theoretically in fields
perpendicular, tilted and parallel to the quantum well plane. Spin and phase
relaxation times are found as functions of temperature and parallel field. It
is demonstrated that spin dephasing is due to the Dresselhaus spin-orbit
interaction. The values of electron spin splittings and spin relaxation times
are found in the wide range of 2D density. Application of in-plane field is
shown to destroy weak antilocalization due to competition of Zeeman and
microroughness effects. Their relative contributions are separated, and the
values of the in-plane electron g-factor and characteristic size of interface
imperfections are found.Comment: 8 pages, 8 figure
Role of doped layers in dephasing of 2D electrons in quantum well structures
The temperature and gate voltage dependences of the phase breaking time are
studied experimentally in GaAs/InGaAs heterostructures with single quantum
well. It is shown that appearance of states at the Fermi energy in the doped
layers leads to a significant decrease of the phase breaking time of the
carriers in quantum well and to saturation of the phase breaking time at low
temperature.Comment: 4 pages, 6 figure
Light emission and spin-polarised hole injection in InAs/GaAs quantum dot heterostructures with Schottky contact
EPL draftWe demonstrate the feasibility to obtain electroluminescence (EL), up to room temperature, from InGaAs self-assembled quantum dots (QDs) included in a forward-biased Schottky
diode. Moreover, using a ferromagnet (FM) as the contact layer, sizable circular polarization of
the EL emission in the presence of an external magnetic eld is obtained. A resonant behav-
ior of the degree of circular polarization (P) as a function of applied voltage (V ), for a given
value of magnetic eld, is observed. We explain our ndings using a model including tunneling
of (spin-polarised) holes through the metal-semiconductor interface, transport in the near surface
region of the heterostructure and out-of-equilibrium statistics of the injected carriers occupying
the available states in the QD heterostructure. In particular, the resonant P(V ) dependence is
related to the splitting of the qusi-Fermi level for two spin orientations in the FM.FCT, Portugal (project
POCI/FIS/58524/2004), the RFBR, Russia (grant 10-02-
00501), MEC (grants MAT2008-01555, QOIT-CSD2006-
00019) and CAM (S-2009/ESP-1503) (Spain)
Giant suppression of the Drude conductivity due to quantum interference in disordered two-dimensional systems
Temperature and magnetic field dependences of the conductivity in heavily
doped, strongly disordered two-dimensional quantum well structures
GaAs/InGaAs/GaAs are investigated within wide conductivity and
temperature ranges. Role of the interference in the electron transport is
studied in the regimes when the phase breaking length crosses over the
localization length with lowering temperature,
where and are the Fermi quasimomentum and mean free path,
respectively. It has been shown that all the experimental data can be
understood within framework of simple model of the conductivity over
delocalized states. This model differs from the conventional model of the weak
localization developed for and by one point: the
value of the quantum interference contribution to the conductivity is
restricted not only by the phase breaking length but by the
localization length as well. We show that just the quantity
rather than
, where is the dephasing time and
, is responsible for the temperature and
magnetic field dependences of the conductivity over the wide range of
temperature and disorder strength down to the conductivity of order .Comment: 11 pages, 15 figure
Diffusion and ballistic contributions of the interaction correction to the conductivity of a two-dimensional electron gas
The results of an experimental study of interaction quantum correction to the
conductivity of two-dimensional electron gas in AB semiconductor
quantum well heterostructures are presented for a wide range of
-parameter (), where is the transport
relaxation time. A comprehensive analysis of the magnetic field and temperature
dependences of the resistivity and the conductivity tensor components allows us
to separate the ballistic and diffusion parts of the correction. It is shown
that the ballistic part renormalizes in the main the electron mobility, whereas
the diffusion part contributes to the diagonal and does not to the off-diagonal
component of the conductivity tensor. We have experimentally found the values
of the Fermi-liquid parameters describing the electron-electron contribution to
the transport coefficients, which are found in a good agreement with the
theoretical results.Comment: 11 pages, 11 figure
The environment effect on operation of in-vessel mirrors for plasma diagnostics in fusion devices
First mirrors will be the plasma facing components of optical diagnostic
systems in ITER. Mirror surfaces will undergo modification caused by erosion
and re-deposition processes [1,2]. As a consequence, the mirror performance may
be changed and may deteriorate [3,4]. In the divertor region it may also be
obscured by deposition [5-7]. The limited access to in-vessel components of
ITER calls for testing the mirror materials in present day devices in order to
gather information on the material damage and degradation of the mirror
performance, i.e. reflectivity. A dedicated experimental programme, First
Mirror Test (FMT), has been initiated at the JET tokamak within the framework
Tritium Retention Studies (TRS).Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France).Submitted by B. Schunke on behalf of V. Voytseny
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