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

Spin-orbit coupling provides a versatile tool to generate and to manipulate the spin degree of freedom in low-dimensional semiconductor structures. The spin Hall effect, where an electrical current drives a transverse spin current and causes a nonequilibrium spin accumulation observed near the sample boundary, the spin-galvanic effect, where a nonequilibrium spin polarization drives an electric current, or the reverse process, in which an electrical current generates a nonequilibrium spin polarization, are all consequences of spin-orbit coupling. In order to observe a spin Hall effect a bias driven current is an essential prerequisite. The spin separation is caused via spin-orbit coupling either by Mott scattering (extrinsic spin Hall effect) or by Rashba or Dresselhaus spin splitting of the band structure (intrinsic spin Hall effect). Here we provide evidence for an elementary effect causing spin separation which is fundamentally different from that of the spin Hall effect. In contrast to the spin Hall effect it does not require an electric current to flow: It is spin separation achieved by spin-dependent scattering of electrons in media with suitable symmetry. We show that by free carrier (Drude) absorption of terahertz radiation spin separation is achieved in a wide range of temperatures from liquid helium up to room temperature. Moreover the experimental results give evidence that simple electron gas heating by any means is already sufficient to yield spin separation due to spin-dependent energy relaxation processes of nonequilibrium carriers.Comment: 19 pages, 4 figures, 1 tabl

Magnetic vortices form the ground state in micron and submicron ferromagnetic disks. By inserting artificial defects (antidots) into a submicron ferromagnetic disk, magnetic vortices can be pinned controllably thus enabling a different way for magnetic switching. We show that by inserting n antidots into a disk magnetization reversal takes place via n-1 jumps of the vortex core between neighboring antidots. This cannot only be used to establish stable two-state switching for n=2, but also to realize a multilevel remanent state with low switching fields.

The introduction of in situ synthesis on the surface of solid substrates has resulted in tremendous progress in different fields of science and technology. Immobilized metallic nanoparticles are of particular interest. Their applications include electrocatalysis, data storage systems, new electronic devices, electrochemical chemo-and biosensors, and refractometric and fluorescent sensors based on plasmon effects. [1][2][3][4] The strategies for the preparation of these systems are mostly based on the deposition of presynthesized nanoparticles with [5] or without [6,7] further treatment. So far the particles have been deposited mostly by the electrospray technique [8] or by adsorption, [6,9] and only a few techniques based on the in situ synthesis of nanoparticle have been tested. Such a synthesis is possible by electroless deposition or by electroplating. The electroless deposition of nanoparticles was used for the deposition of gold, silver, nickel, palladium, copper, and cobalt nanoparticles onto different substrates. [1,2,10,11] Deposition by electroplating was used for formation of bulk phases of nanocrystalline metals by the reduction of corresponding salts in ionic liquids. [12,13] Formation of metallic nanoparticles by electrochemical reduction on the tip of a scanning tunneling microscope (STM) followed by transfer to planar metal electrodes was reported [14,15] and then reproduced by other groups.[16] Here, we describe an alternative approach for the preparation of metallic nanoparticles on electrode surfaces that does not require STM. Our approach is based on the reduction of metals on nanoelectrodes formed by the recently developed spreader-bar technique. [17] We tested the approach for the deposition of platinum and copper nanoparticles but do not see any principal limitations for its extension to other conductive or semiconductive materials such as metals, electrochemically synthesized polymers, and nanocomposites. The size of the nanoparticles can be controlled by the value of the reduction charge. In the present work the nanoparticles are between 20 and 1000 nm, but smaller particles are most likely possible.The spreader-bar technique [17] is based on the coadsorption of two types of molecules: long-chain matrix molecules and large rigid planar molecules (templates or molecular spreader-bars). This results in the fabrication of heterogeneous monomolecular film in which the spreader-bar moieties are imbedded in the matrix. In contrast to two-dimensional molecular imprinting, the structures formed by this technique are permanently stable, because the spreader-bar molecules remain in the monolayer. This approach was successfully applied to generate stable artificial receptors for different purines and pyrimidines.[18] Also, the formation of enantioselective receptors was reported. [19] In the present work, the spreader-bar approach was used to design a nanostructured self-assembled monolayer (SAM) consisting of insulating matrix (long-chain alkylthiols) with incorporated conductive "islands" (large, p...

Magnetoresistive elements for data storage or logic operations require reliable bistable magnetic switching. Soft magnetic nanodisks containing two antidots, which serve as pinning sites for a magnetic vortex, provide an alternative route for bistable magnetic switching. Here we show by means of micromagnetic simulations that field pulses generated by two orthogonal metallic current lines can switch the magnetic vortex core between antidots on a subnanosecond time scale. Using a third strip line to enable switching of the element’s magnetically hard layer, the logic operations AND, OR, NAND, and NOR can be established.