1,044 research outputs found
Spin Photovoltaic Effect in Quantum Wires with Rashba Interaction
We propose a mechanism for spin polarized photocurrent generation in quantum
wires. The effect is due to the combined effect of Rashba spin-orbit
interaction, external magnetic field and microwave radiation. The
time-independent interactions in the wire give rise to a spectrum asymmetry in
k-space. The microwave radiation induces transitions between spin-splitted
subbands, and, due to the peculiar energy dispersion relation, charge and spin
currents are generated at zero bias voltage. We demonstrate that the generation
of pure spin currents is possible under an appropriate choice of external
control parameters
Experimental demonstration of associative memory with memristive neural networks
When someone mentions the name of a known person we immediately recall her face and possibly many other traits. This is because we possess the so-called associative memory - the ability to correlate different memories to the same fact or event. Associative memory is such a fundamental and encompassing human ability (and not just human) that the network of neurons in our brain must perform it quite easily. The question is then whether electronic neural networks - electronic schemes that act somewhat similarly to human brains - can be built to perform this type of function. Although the field of neural networks has developed for many years, a key element, namely the synapses between adjacent neurons, has been lacking a satisfactory electronic representation. The reason for this is that a passive circuit element able to reproduce the synapse behaviour needs to remember its past dynamical history, store a continuous set of states, and be "plastic" according to the pre-synaptic and post-synaptic neuronal activity. Here we show that all this can be accomplished by a memory-resistor (memristor for short). In particular, by using simple and inexpensive off-the-shelf components we have built a memristor emulator which realizes all required synaptic properties. Most importantly, we have demonstrated experimentally the formation of associative memory in a simple neural network consisting of three electronic neurons connected by two memristor-emulator synapses. This experimental demonstration opens up new possibilities in the understanding of neural processes using memory devices, an important step forward to reproduce complex learning, adaptive and spontaneous behaviour with electronic neural networks
Radiation-induced current in quantum wires with side-coupled nano-rings
Photocurrent generation is studied in a system composed of a quantum wire
with side-coupled quantum rings. The current generation results from the
interplay of the particular geometry of the system and the use of circularly
polarized radiation. We study the energy-momentum conservation for optical
transitions involving electrons moving forwards and backwards in the wire. Due
to the lack of time-reversal symmetry in the radiation, the optical transitions
depend on the direction of motion of the electrons, leading to a current at
zero bias voltage. The photocurrent increases with the number of rings within a
wide range of physical parameters. A weak non-linear dependence of the current
in the number of rings, related to quantum interference effects, is also
predicted. This geometry suggests a scalable method for the generation of
sizeable photocurrents based on nanoscale components.Comment: 7 pages, 6 figure
Drift-Diffusion Approach to Spin-Polarized Transport
We develop a drift-diffusion equation that describes electron spin
polarization density in two-dimensional electron systems. In our approach,
superpositions of spin-up and spin-down states are taken into account, what
distinguishes our model from the traditional two-component drift-diffusion
approximation. The Dresselhaus and Rashba spin-orbit coupling mechanisms are
incorporated into consideration, as well as an applied electric field. The
derived equation is applied to the modelling of relaxation of homogeneous spin
polarization. Our results are consistent with previous studies
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