89 research outputs found
Stroboscopic wave packet description of time-dependent currents through ring-shaped nanostructures
We present an implementation of a new method for explicit simulations of
time-dependent electric currents through nanojunctions. The method is based on
unitary propagation of stroboscopic wave packet states and is designed to treat
open systems with fluctuating number of electrons while preserving full quantum
coherence throughout the whole infinite system. We demonstrate the performance
of the method on a model system consisting of a ring-shaped nanojunction with
two semi-infinite tight-binding leads. Time-dependent electron current
responses to abrupt bias turn-on or gate potential switching are computed for
several ring configurations and ring-leads coupling parameters. The found
current-carrying stationary states agree well with the predictions of the
Landauer formula. As examples of genuinely time-dependent process we explore
the presence of circulating currents in the rings in transient regimes and the
effect of a time-dependent gate potential.Comment: corrections of typos compared to the previous versio
Edge-induced spin polarization in two-dimensional electron gas
We characterize the role of the spin-orbit coupling between electrons and the confining potential of the edge in nonequilibrium two-dimensional homogeneous electronic gas. We derive a simple analytical result for the magnitude of the current-induced spin polarization at the edge and prove that it is independent of the details of the confinement edge potential and the electronic density within realistic values of the parameters of the considered models. While the amplitude of the spin accumulation is comparable to the experimental values of extrinsic spin-Hall effect in similar samples, the spatial extent of edge-induced effect is restricted to the distances on the order of Fermi wavelength (similar to 10 nm)
Stroboscopic wave-packet description of nonequilibrium many-electron problems
We introduce the construction of an orthogonal wave-packet basis set, using the concept of stroboscopic time propagation, tailored to the efficient description of nonequilibrium extended electronic systems. Thanks to three desirable properties of this basis, significant insight is provided into nonequilibrium processes (both time-dependent and steady-state), and reliable physical estimates of various many-electron quantities such as density, current, and spin polarization can be obtained. Use of the wave-packet basis provides new results for time-dependent switching-on of the bias in quantum transport, and for current-induced spin accumulation at the edge of a 2D doped semiconductor caused by edge-induced spin-orbit interaction
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