Péter Földi

Quantum rings as electron spin beam splitters

Quantum interference and spin-orbit interaction in a one-dimensional mesoscopic semiconductor ring with one input and two output leads can act as a spin beam splitter. Different polarization can be achieved in the two output channels from an originally totally unpolarized incoming spin state, very much like in a Stern-Gerlach apparatus. We determine the relevant parameters such that the device has unit efficiency.

Networks of quantum nanorings: programmable spintronic devices.

An array of quantum rings with local (ring by ring) modulation of the spin orbit interaction (SOI) can lead to novel effects in spin state transformation of electrons. It is shown that already small (3 x 3, 5 x 5) networks are remarkably versatile from this point of view: Working in a given network geometry, the input current can be directed to any of the output ports, simply by changing the SOI strengths by external gate voltages. Additionally, the same network with different SOI strengths can be completely analogous to the Stern-Gerlach device, exhibiting spatial-spin entanglement.

Stability of spintronic devices based on quantum ring networks

Transport properties in mesoscopic networks are investigated, where the strength of the (Rashba-type) spin-orbit coupling is assumed to be tuned with external gate voltages. We analyze in detail to what extent the ideal behavior and functionality of some promising network-based devices are modified by random (spin-dependent) scattering events and by thermal fluctuations. It is found that although the functionality of these devices is obviously based on the quantum coherence of the transmitted electrons, there is a certain stability: moderate level of errors can be tolerated. For mesoscopic networks made of typical semiconductor materials, even cryogenic temperatures can smear out the desired transport properties. When the energy distribution of the input carriers is narrow enough, it turns out that the devices can operate close to their ideal limits even at relative high temperature. As an example, we present results for two different networks: one that realizes a Stern-Gerlach device and another that simulates a spin quantum walker. Finally we propose a simple network that can act as a narrow band energy filter even in the presence of random scatterers.

Spatial interference induced spin polarization in a three-terminal quantum ring

We present an exact, analytic solution of the spin dependent quantum transport problem with spin-orbit interaction in a one-dimensional mesoscopic ring with one input and two output leads. We demonstrate that for appropriate parameters spatial interference in the ring leads to a behavior analogous to that of the Stern-Gerlach apparatus: different spin polarizations can be achieved in the two output channels from an originally totally unpolarized incoming spin state. It is shown that this requires an appropriate interference of states that carry oppositely directed currents. We find that spin polarization is possible for several geometries, including the case when the device is not symmetric with respect to the incoming lead. A clear connection is established between the Stern-Gerlach like property of the device and the relevant Aharonov-Casher phases in the loop geometry.

The effect of dynamical Bloch oscillations on optical-field-induced current in a wide-gap dielectric

We consider the motion of charge carriers in a bulk wide-gap dielectric interacting with a few-cycle laser pulse. A semiclassical model based on Bloch equations is applied to describe the emerging time-dependent macroscopic currents for laser intensities close to the damage threshold. At such laser intensities, electrons can reach edges of the first Brillouin zone even for electron-phonon scattering rates as high as those known for SiO2. We find that, whenever this happens, Bragg-like reflections of electron waves, also known as Bloch oscillations, affect the dependence of the charge displaced by the laser pulse on its carrier-envelope phase.

Magnetoconductance of rectangular arrays of quantum rings

Electron transport through multi-terminal rectangular arrays of quantum rings is studied in the presence of Rashba-type spin-orbit interaction (SOI) and of a perpendicular magnetic field. Using the analytic expressions for the transmission and reflection coefficients for single rings we obtain the conductance through such arrays as a function of the SOI strength, the magnetic flux, and of the wave vector

Time evolution in the Morse potential using supersymmetry: Dissociation of the NO molecule

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Few-cycle plasmon oscillations controlling photoemission from metal nanoparticles

of the incident electron. Due to destructive or constructive spin interferences caused by the SOI, the array can be totally opaque for certain ranges of

Gauge invariance and interpretation of interband and intraband processes in high-order harmonic generation from bulk solids

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Two-dimensional quantum rings with oscillating spin-orbit interaction strength: A wave function picture

, while there are parameter values where it is completely transparent. Spin resolved transmission probabilities show nontrivial spin transformations at the outputs of the arrays. When point-like random scattering centers are placed between the rings, the Aharonov-Bohm peaks split, and an oscillatory behavior of the conductance emerges as a function of the SOI strength.