98 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
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
Neuromorphic, Digital and Quantum Computation with Memory Circuit Elements
Memory effects are ubiquitous in nature and the class of memory circuit
elements - which includes memristors, memcapacitors and meminductors - shows
great potential to understand and simulate the associated fundamental physical
processes. Here, we show that such elements can also be used in electronic
schemes mimicking biologically-inspired computer architectures, performing
digital logic and arithmetic operations, and can expand the capabilities of
certain quantum computation schemes. In particular, we will discuss few
examples where the concept of memory elements is relevant to the realization of
associative memory in neuronal circuits, spike-timing-dependent plasticity of
synapses, digital and field-programmable quantum computing
Emulation of floating memcapacitors and meminductors using current conveyors
We suggest circuit realizations of emulators transforming memristive devices
into effective floating memcapacitive and meminductive systems. The emulator's
circuits are based on second generation current conveyors and involve either
four single-output or two dual-output current conveyors. The equations
governing the resulting memcapactive and meminductive systems are presented.Comment: Electronics Letters (in press
Accumulation of Electron Spin Polarization at Semiconductor Interfaces
In this Brief Report we study theoretically the propagation of electron spin polarization through an interface separating two n-type semiconductor regions within the two-component drift-diffusion model in an applied electric field. It is assumed that inhomogeneous spin polarization is created locally by a continuous source of spin polarization and is driven through the boundary by the electric field. The spin polarization distribution is calculated analytically. We find that for specific values of parameters describing the system, the electron spin polarization is accumulated near the interface. A simple analytical expression for the amplitude of spin accumulation as a function of the system parameters is found. The obtained results will be useful in designing new spintronic devices
Long-Lived Spin Coherence States in Semiconductor Heterostructures
We study evolution of electron spin coherence having nonhomogeneous direction of spin polarization vector in semiconductor heterostructures. It is found that the electron spin relaxation time due to the D’yakonov- Perel’ relaxation mechanism essentially depends on the initial spin polarization distribution. This effect has its origin in the coherent spin precession of electrons diffusing in the same direction. We predict a long spin relaxation time of a novel structure: a spin coherence standing wave and discuss its experimental realization
Optically Induced Suppression of Spin Relaxation in Two-Dimensional Electron Systems with Rashba Interaction
A pulsed technique for electrons in two-dimensional systems, in some ways analogous to spin echo in nuclear magnetic resonance, is discussed. We show that a sequence of optical below-band-gap pulses can be used to suppress the electron spin relaxation due to the D’yakonov-Perel’ spin relaxation mechanism. The spin relaxation time is calculated for several pulse sequences within a Monte Carlo simulation scheme. The maximum of the spin relaxation time as a function of magnitude or width of the pulses corresponds to a π pulse. It is important that even relatively distant pulses efficiently suppress spin relaxation
Electronic Structure of Nuclear-Spin-Polarization-Induced Quantum Dots
We study a system in which electrons in a two-dimensional electron gas are confined by a nonhomogeneous nuclear-spin polarization. The system consists of a heterostructure that has nonzero nuclei spins. We show that in this system electrons can be confined into a dot region through a local nuclear-spin polarization. The nuclear-spin-polarization-induced quantum dot has interesting properties indicating that electron energy levels are time dependent because of the nuclear-spin relaxation and diffusion processes. Electron confining potential is a solution of diffusion equation with relaxation. Experimental investigations of the time dependence of electron energy levels will result in more information about nuclear-spin interactions in solids
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