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