Sign-reversal of drag in bilayer systems with in-plane periodic potential modulation

We develop a theory for describing frictional drag in bilayer systems with in-plane periodic potential modulations, and use it to investigate the drag between bilayer systems in which one of the layers is modulated in one direction. At low temperatures, as the density of carriers in the modulated layer is changed, we show that the transresistivity component in the direction of modulation can change its sign. We also give a physical explanation for this behavior.Comment: 4 pages, 4 figure

Observation of Parity Violation in the Omega-minus -> Lambda + K-minus Decay

The alpha decay parameter in the process Omega-minus -> Lambda + K-minus has been measured from a sample of 4.50 million unpolarized Omega-minus decays recorded by the HyperCP (E871) experiment at Fermilab and found to be [1.78 +/- 0.19(stat) +/- 0.16(syst)]{\times}10^{-2}. This is the first unambiguous evidence for a nonzero alpha decay parameter, and hence parity violation, in the Omega-minus -> Lambda + K-minus decay.Comment: 10 pages, 7 figure

Magnetotransport in Two-Dimensional Electron Systems with Spin-Orbit Interaction

We present magnetotransport calculations for homogeneous two-dimensional electron systems including the Rashba spin-orbit interaction, which mixes the spin-eigenstates and leads to a modified fan-chart with crossing Landau levels. The quantum mechanical Kubo formula is evaluated by taking into account spin-conserving scatterers in an extension of the self-consistent Born approximation that considers the spin degree of freedom. The calculated conductivity exhibits besides the well-known beating in the Shubnikov-de Haas (SdH) oscillations a modulation which is due to a suppression of scattering away from the crossing points of Landau levels and does not show up in the density of states. This modulation, surviving even at elevated temperatures when the SdH oscillations are damped out, could serve to identify spin-orbit coupling in magnetotransport experiments. Our magnetotransport calculations are extended also to lateral superlattices and predictions are made with respect to 1/B periodic oscillations in dependence on carrier density and strength of the spin-orbit coupling.Comment: 8 pages including 8 figures; submitted to PR

Negative differential resistance of a 2D electron gas in a 1D miniband

We experimentally investigate the miniband transport in a novel kind of superlattice fabricated by the “cleaved edge overgrowth” method. The structure represents a field effect transistor, where the channel consists of an MBE-grown superlattice perpendicular to the current flow. By means of the gate the Fermi energy can be adjusted between the bottom of the first miniband and into the minigap. We observe pronounced negative differential resistance at electric fields across the superlattice as low as 160 V/cm. From magnetotransport measurements a relation between the applied gate voltage and the position of the Fermi energy in the artificial band structure is established. Electron mobility depending on the Fermi energy is deduced separately from Shubnikov–de Haas oscillations, from the voltage at the peak current and from the low-field resistance

Breakdown of Shubnikov–de Haas oscillations in a short-period 1D lateral superlattice

Magnetic breakdown is observed in a two-dimensional electron system subject to a strong, atomically precise, one-dimensional potential with a period of 15 nm. The transition from closed to open electron orbits is studied in magnetotransport experiments by continuously changing the Fermi energy of the superlattice within and above the first miniband. Shubnikov–de Haas oscillations quench for Fermi energies close to the miniband gap but recover at higher magnetic fields. The density of states is clearly altered from a conventional 2D system which manifests itself in aperiodic magnetooscillations when sweeping the Fermi energy at fixed magnetic fields