A. Bringer

Electronic state-lifetime interference observed at Ne K inter-resonance excitation

Abstract Electronic decay spectra of Ne, excited at the 1s threshold have been measured. Final states of the 2p −2 n ′p configuration are reached via 1s −1 n p intermediate states. Appreciable intensity from spectator shake transitions ( n ≠ n ′) is found and the predictions of a simple intensity model are evaluated. The model reproduces the experimental results at on-resonance excitation. At inter-resonance excitation an apparent excitation energy dependence of the shake probability is accounted for by electronic state-lifetime interference theory.

Magnetic adatom induced Skyrmion-like spin texture in surface electron waves.

When a foreign atom is placed on a surface of a metal, the surrounding sea of electrons responds by screening the additional charge leading to oscillations or ripples. On surfaces, those electrons are sometimes confined to two-dimensional surface states, whose spin-degeneracy is lifted due to the Rashba effect arising from the spin-orbit interaction of electrons and the inversion asymmetric environment. It is believed that at least for a single adatom scanning tunneling microscopy measurements are insensitive to the Rashba splitting; i.e., no signatures in the charge oscillations will be observed. Resting on scattering theory, we demonstrate that, if magnetic, one single adatom is enough to visualize the presence of the Rashba effect in terms of an induced spin magnetization of the surrounding electrons exhibiting a twisted spin texture described as superposition of two Skyrmionic waves of opposite chirality.

Density depletion profile and solvation free energy of a colloidal particle in a polymer solution

The solvation free energy and polymer density depletion profile of a single mesoscopic colloidal particle in a solution of free nonadsorbing polymer chains are investigated theoretically. Keeping both the particle to polymer size ratio and the degree of inter-chain overlap arbitrary, we see how the qualitatively different behavior evolves in the limits of small and large size ratios and of dilute and semidilute solutions. While most of our results are obtained within a mean-field approach, we also use a “renormalized tree approximation” to estimate the surface tension and the coefficient of spontaneous curvature in a Helfrich expansion for large particle to polymer size ratio. There is a weak maximum in the polymer density profile for arbitrary size ratio. For small size ratio the maximum can be explained in terms of a minimum in the bulk polymer density correlation function.

Integral properties of channel interference in resonant X-ray scattering

Abstract The integral properties of channel interference in resonant X-ray scattering (RXS) are formally investigated. The qualitative difference between vibrational and electronic state lifetime interference is elucidated. It is shown that the integral interference term in the RXS cross section summed over all intermediate and final states is exactly equal to zero. A few experimental cases are given as illustration. As a result of numerical simulations it is found that the integral interference term is also close to zero if only certain finite sets of intermediate and final states are taken into account.

Rashba effect in InGaAs∕InP parallel quantum wires

We report on the Rashba effect in InGaAs∕InP quantum wires with an effective width ranging from 1.18μm down to 210nm. By measuring 160 wires in parallel universal conductance, fluctuations could be suppressed so that the characteristic beating effect in the magnetorestistance was observable down to very low magnetic fields. A characteristic shift of the nodes in the beating pattern was found for decreasing wire width. By assuming a realistic soft-wall potential, the experimentally observed node positions could be reproduced. For the range of measured wires, our study confirms that the Rashba coupling parameter does not change with wire width.

Interpreting magnetization from Faraday rotation in birefringent magnetic media

The Faraday effect is an extremely useful probe of magnetization dynamics on an ultrafast scale. However, the measured Faraday rotation is difficult to interpret in birefringent media. We investigate the link between magnetization and Faraday rotation by solving Maxwell’s equations in a magnetically ordered, birefringent material. We find that the Faraday rotation can depend nonlinearly on the magnetization, meaning that symmetric magnetic oscillations may lead to asymmetric Faraday measurements. Furthermore, sample alignment becomes important—if the incident light is not polarized along a birefringence axis of the sample, the Faraday rotation may be strongly enhanced or weakened, and the interpretation of the magnetization amplitude may be wrong by an order of magnitude.

Wave packet study of a linear collision problem

Using real‐time wave packet propagation we consider the scattering properties of a linear collision system consisting of a harmonic oscillator coupled by truncated Morse potentials to two particles. This system is viewed as a model for the collision of a projectile D with a three particle target ABC with interactions such that the possible final states comprise backscattering of the projectile with the target intact, the ‘‘exchange’’ reaction ABC+D→A+BCD and the ‘‘fragmentation’’ reaction ABC+D→A+BC+D. For the types of interaction considered, the exchange reaction was found to proceed primarily via inelastic resonant processes and to be the dominant event for incident energies below the oscillator energy. Fragmentation occurred via nonresonant processes and dominated at higher energy. Other features of the scattering are discussed and compared with simple quantum theory and the description of the system given by classical mechanics.

Spin–orbit coupling in GaxIn1−xAs/InP two-dimensional electron gases and quantum wire structures

In this work, the effect of spin–orbit coupling in two-dimensional electron gases and quantum wire structures is discussed. First, the theoretical framework is introduced including spin–orbit coupling due to structural inversion asymmetry, the so-called Rashba effect, as well as the Dresselhaus term. The latter originates from bulk inversion asymmetry. With regard to wire structures, special attention is devoted to the influence of the particular shape of the confinement potential on the energy spectrum. As a model system GaxIn1−xAs/InP heterostructures are chosen, where different thicknesses of the strained Ga0.23In0.77As channel layer were introduced, in order to adjust the strength of the spin–orbit coupling. Hall bar structures as well as sets of identical wires with different widths were prepared. In two-dimensional electron gases, the strength of the spin–orbit coupling was extracted by analyzing the characteristic beating pattern in the Shubnikov–de Haas oscillations. In addition, the weak antilocalization was utilized to obtain information on the spin–orbit coupling. It is shown that for decreasing width of the strained layer the Rashba effect, which dominates in our layer systems, is increased. This behavior is attributed to the larger interface contribution if the electron wavefunction is strongly confined. The measurements on the wire structures revealed a transition from weak antilocalization to weak localization if the wire width is decreased. This effect is attributed to an enhanced spin diffusion length for strongly confined systems.

Wavepacket study of a charge transfer system

Abstract The transfer of charge when an atom or ion strikes a surface is considered within a simple model where both ion and electron can be treated fully quantum mechanically and on the same footing. Results for the dependence of the charge transfer on incident energy and potential parameters show that the predictions of a standard model where the ion is assumed to follow a classical trajectory and the charge transfer described in terms of a level width are in general quite reliable. Charge transfer also occurs via inelastic “shake-up” processes. We show that the behaviour of this fraction can be understood within a trajectory model where the action of the surface on the bound electron is treated via a time-dependent force.

Ballistic and spin transport in InAs nanowires

The transport in InAs nanowires is investigated at low temperatures. On wires with different n-type doping information on Rashba and Dresselhaus spin-orbit coupling is gained from weak antilocalization measurements. By using a short local gate quantum point contacts are formed, which show quantized conductance. From bias-depended measurements the g-factor is extracted for different subbands.