We have introduced an artificial array of scatterers into a macroscopic two-dimensional conductor nearly devoid intrinsic defects. This generates pronounced structure in the magnetoresistance, anomalous low-field Hall plateaus, and quenching effect about B=0. Our calculations show that predominant features data arise from commensurate classical orbits impaled upon small groups imposed scatterers.

A novel type of magnetoresistance oscillations is observed in high-mobility AlGaAs/GaAs heterojunctions with a holographically induced lateral periodic modulation one direction. Theoretically, the effect shown to result from an oscillatory dependence bandwidth modulation-broadened Landau levels two-dimensional electron system on band index, which leads samples strongly anisotropic oscillating contribution conductivity tensor. The oscillations, ${\mathrm{B}}^{\mathrm{\ensuremath{-}}1}$,...

A new type of magnetoresistance oscillation periodic in 1/B is observed when the carrier density Ns a two-dimensional electron gas weakly modulated with period smaller than mean free path electrons. Experiments high mobility AlGaAs-GaAs heterojunctions where by holographic illumination at T ⩽ 4.2 K show that additional quantum determined separation interference fringes. This corresponds to Shubnikov-de Haas oscillations only electrons within first reduced Brillouin zone |k| < π/a contribute.

The relative strengths of Rashba and Dresselhaus terms describing the spin-orbit coupling in semiconductor quantum well (QW) structures are extracted from photocurrent measurements on $n$-type InAs QWs containing a two-dimensional electron gas (2DEG). This novel technique makes use angular distribution spin-galvanic effect at certain directions spin orientation plane QW. ratio relevant coefficients can be deduced directly experiment does not relay theoretically obtained quantities. Thus our...

The deposition of ferromagnetic microstructures on top a high-mobility two-dimensional electron gas (2DEG) allows the investigation transport in periodic magnetic field which alternates length scale small compared to elastic mean free path electrons. longitudinal resistance 2DEG displays, as function externally applied field, long-predicted commensurability oscillations result from interplay between two characteristic scales system, classical cyclotron radius ${R}_{c}$ electrons and period...

A nonequilibrium population of spin-up and spin-down states in quantum well structures has been achieved applying circularly polarized radiation. The spin polarization results a directed motion free carriers the plane perpendicular to direction light propagation. Because selection rules current is determined by helicity can be reversed switching from right left handed. microscopic model presented which describes origin photon driven current. suggests that system behaves as battery generates

The resistivity ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{x}}$ measured in large antidot arrays as a function of an applied perpendicular magnetic field B displays distinct quantum oscillations at very low temperatures. These characteristically differ from conventional Shubnikov-de Haas which are periodic 1/B. A crossover to discloses the influence imposed potential. Applying semiclassical orbit theory nonintegrable (chaotic) electron motion lattice we attribute these phenomena...

We explore the magnetization pattern of Co and permalloy disks with diameters between 80 nm 1 μm by using two complementary experimental techniques: Lorentz microscopy magnetic force (MFM). By means we show that dominating is a vortex structure closed flux lines in plane disks. Complementary MFM measurements demonstrate center tilted out disk. The findings closely agree corresponding micromagnetic calculations.

The energy spectrum of a two-dimensional electron system in perpendicular homogeneous magnetic field and weak lateral superlattice potential with square symmetry is composed Landau bands recursive internal subband structure. Hall conductance the minigaps anticipated to be quantized integer multiples ${e}^{2}/h$ that vary erratically from minigap accordance Diophantine equation. measurements on samples requisite properties uncover this long searched for evidence Hofstadter's butterflylike spectrum.

Thin-circular lithographically defined magnetic elements with a spin vortex configuration are excited short perpendicular field pulse. We report the first images of eigenmodes up to third order, obtained by means phase sensitive Fourier transform imaging technique. Both axially symmetric and symmetry breaking azimuthal observed. observe strong oscillations magnetization in central part elements. The experimental data good agreement micromagnetic simulations.

Single- and few-layer MoS2 has recently gained attention as an interesting material system for opto-electronics. Here, we report on scanning Raman measurements flakes prepared by exfoliation. We observe a mode corresponding to rigid shearing oscillation of adjacent layers. This appears at very low shifts between 20 30 cm−1. Its position strongly depends the number layers, which independently determine using atomic force microscopy investigation other characteristic modes. spectroscopy shear...

We report the observation of tunneling anisotropic magnetoresistance effect (TAMR) in epitaxial metal-semiconductor system Fe/GaAs/Au. The observed two-fold anisotropy resistance can be switched by reversing bias voltage, suggesting that originates from interference spin-orbit coupling at interfaces. Corresponding model calculations reproduce experimental findings very well.

We report the observation of circular ac Hall effect where current is solely driven by crossed electric and magnetic fields circularly polarized radiation. Illuminating an unbiased monolayer sheet graphene with terahertz radiation at room temperature generates--under oblique incidence--an perpendicular to plane incidence, whose sign reversed switching helicity. Alike classical dc effect, voltage caused E B which are, however rotating light's frequency.

The spin-galvanic effect and the circular photogalvanic induced by terahertz radiation are applied to determine relative strengths of Rashba Dresselhaus band spin splitting in (001)-grown GaAs InAs based two dimensional electron systems. We observed that shifting $\ensuremath{\delta}$-doping plane from one side quantum well other results a change sign photocurrent caused while term remains. measurements give necessary feedback for technologists looking structures with equal splittings or...

We fabricated and measured antidot lattices in single layer graphene with lattice periods down to 90 nm. In large-period lattices, a well-defined quantum Hall effect is observed. Going smaller spacings the gradually disappears, following geometric size effect. Lattices narrow constrictions between antidots behave as networks of nanoribbons, showing high-resistance state transport gap few mV around Dirac point. observe pronounced weak localization magnetoresistance, indicating strong...

We present an ultrafast graphene-based detector, working in the THz range at room temperature. A logarithmic-periodic antenna is coupled to a graphene flake that produced by exfoliation on SiO2. The detector was characterized with free-electron laser FELBE for wavelengths from 8 um 220 um. rise time 50 ps wavelength 30 Autocorrelation measurements exploiting nonlinear photocurrent response high intensities reveal intrinsic below 10 ps. This has potential characterizing temporal overlaps, e....

In layered semiconductors with spin-orbit interaction (SOI) a persistent spin helix (PSH) state suppressed relaxation is expected if the strengths of Rashba and Dresselhaus SOI terms, $\ensuremath{\alpha}$ $\ensuremath{\beta}$, are equal. Here we demonstrate gate control detection PSH in two-dimensional electron systems strong including terms cubic momentum. We consider strain-free InGaAs/InAlAs quantum wells first determine ratio $\ensuremath{\alpha}/\ensuremath{\beta}\ensuremath{\simeq}1$...

We observe photocurrents induced in single-layer graphene samples by illumination of the edges with circularly polarized terahertz radiation at normal incidence. The photocurrent flows along sample and forms a vortex. Its winding direction reverses switching light helicity from left to right handed. demonstrate that stems edges, which reduce spatial symmetry result an asymmetric scattering carriers driven electric field. developed theory based on Boltzmann's kinetic equation is good...

Experimental and theoretical studies on ratchet effects in graphene with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented. A superlatice deposited top monolayer is formed either periodically repeated metal stripes having different widths spacings or inter-digitated comb-like dual-grating-gate (DGG) structures. We show that the photocurrent radiation sensitive to polarization state can be efficiently controlled back gate driving system...

By combining magnetic transmission x-ray microscopy with a stroboscopic pump and probe technique using synchrotron radiation we are able to image the magnetization dynamics in micron sized particles on sub-100 ps time scale lateral spatial resolution down 21 nm. We report first observations squared elements indicating locally varying precessional frequencies which agreement micromagnetic simulations. The experiment opens route towards high spatiotemporal of spin patterns is needed understand...

We present experimental and theoretical results on magnetoresistivity oscillations of high-mobility two-dimensional electron systems in a weak superlattice potential. Experimentally, the band conductivity sample with holographically produced grid potential is shown to be considerably smaller than that same similar linear grating lattice constant. This explained by magnetotransport theory due consideration collision broadening effects peculiar subband splitting Landau levels resulting...