Oscillating spin-orbit interaction in two-dimensional superlattices: sharp transmission resonances and time-dependent spin polarized currents

We consider ballistic transport through a lateral, two-dimensional superlattice with experimentally realizable, sinusoidally oscillating Rashba-type spin-orbit interaction. The periodic structure of the rectangular lattice produces a spin-dependent miniband structure for static SOI. Using Floquet theory, transmission peaks are shown to appear in the mini-bandgaps as a consequence of the additional, time-dependent SOI. A detailed analysis shows that this effect is due to the generation of harmonics of the driving frequency, via which e.g., resonances that cannot be excited in the case of static SOI become available. Additionally, the transmitted current shows space and time-dependent partial spin-polarization, in other words, polarization waves propagate through the superlattice.Comment: 8 pages, 6 figure

Oscillating spin-orbit interaction as a source of spin-polarized wave packets in two-terminal nanoscale devices

Ballistic transport through nanoscale devices with time-dependent Rashba-type spin-orbit interaction (SOI) can lead to spin-polarized wave packets that appear even for completely unpolarized input. The SOI that oscillates in a finite domain generates density and spin polarization fluctuations that leave the region as propagating waves. Particularly, spin polarization has space and time dependence even in regions without SOI. Our results are based on an analytic solution of the time-dependent Schr\"odinger equation. The relevant Floquet quasi-energies that are obtained appear in the energy spectrum of both the transmitted and reflected waves.Comment: 13 pages, 5 figures (IOP preprint style); v2: 15 pages and 6 figures. Subsec. 3.4, a figure and new references have been adde

Thick brane solutions and topology change transition on black hole backgrounds

We consider static, axisymmetric, thick brane solutions on higher dimensional, spherically symmetric black hole backgrounds. It was found recently [1], that in cases when the thick brane has more than 2 spacelike dimensions, perturbative approaches break down around the corresponding thin solutions for Minkowski type topologies. This behavior is a consequence of the fact that thin solutions are not smooth at the axis, and for a general discussion of possible phase transitions in the system, one needs to use a non-perturbative approach. In the present paper we provide an exact, numerical solution of the problem both for black hole- and Minkowski type topologies with arbitrary number of brane and bulk dimensions. We also illustrate a topology change transition in the system for a 5-dimensional brane embedded in a 6-dimensional bulk.Comment: 11 pages, 10 figures, accepted for publication in Phys. Rev.

Reviving Horndeski Theory using Teleparallel Gravity after GW170817

Horndeski gravity was highly constrained from the recent gravitational wave observations by the LIGO Collaboration down to $|c_{g}/c-1|\gtrsim 10^{-15}$. In this Letter we study the tensorial perturbations in a flat cosmological background for an analogue version of Horndenki gravity which is based in Teleparallel Gravity constructed from a flat manifold with a nonvanishing torsion tensor. It is found that in this approach, one can construct a more general Horndeski theory satisfying $c_T=c_g/c=1$ without eliminating the coupling functions $G_5(\phi,X)$ and $G_4(\phi,X)$ that were highly constrained in standard Horndeski theory. Hence, in the Teleparallel approach one is able to restore these terms, creating an interesting way to revive Horndeski gravity.Comment: 12 pages, 0 figure