C. Steinebach

Low temperature scanning tunneling spectroscopy on InAs(110)

Abstract We review our recent work on low temperature scanning tunneling spectroscopy (STS) in magnetic field on InAs(110). First, we describe the influence of the tip on the sample. It results in band bending at the InAs-surface, more precisely in a so called tip induced quantum dot. STS of the quantum dot states is used to reconstruct the quantum dot potential, a major requirement for all further measurements. Second, we analyze the appearance of ionized dopants in constant current images within a simple model based on the local band bending approach. Third, we show scattering states of ionized dopants at different energies appearing in normalized d I /d U -images. Comparison with calculated scattering states in the Wentzel–Kramers–Brillouin (WKB)-approximation gives good correspondance and a good estimate of the depth of individual dopants beneath the surface. Finally, we discuss the energy quantization of the unoccupied states of the tip induced quantum dot in magnetic field. The corresponding d I /d U -curves exhibit peaks attributed to the Landau quantization and the spin splitting of the quantum dot.

Edge spin-density modes in quantum dots in a magnetic field

Abstract We investigate electronic excitations in GaAs–AlGaAs quantum dots by means of resonant inelastic light scattering in the presence of an external magnetic field B . At magnetic field B =0, we observe a series of discrete electronic excitations, namely, charge-density excitations (CDE i ) and spin-density excitations (SDE i ), in one and the same quantum dot sample. We find at finite magnetic field, additionally to the well-known splitting of the CDE i modes (plasmons), a quite similar splitting of the lowest SDE mode whose energy is very close to the single-particle level spacing in the quantum dot. In analogy to the edge magnetoplasmon, we call this excitation an edge spin-density mode.

Coulomb-interaction induced crossover from confined to bulk quantum-dot states in a magnetic field

We have employed inelastic light scattering to investigate electronic excitations of quantum dots in a magnetic field. For small magnetic fields the dispersion of the single-particle excitations (SPEs) follows the Fock–Darwin behavior. But already at moderate fields of Bgreater-or-equal, slanted0.6 T the SPEs deviate from that dispersion and follow directly the cyclotron resonance. This finding is explained by Coulomb-interaction-induced formation of bulk states in the center of the dot. Self-consistent ground-state calculations within the local-density approximation reproduce this result.

Manifestation of the magnetic depopulation of one-dimensional subbands in the optical absorption of acoustic magnetoplasmons in side-gated quantum wires

Abstract We have investigated experimentally and theoretically the far-infrared (FIR) absorption of gated, deep-mesa-etched GaAs/AlxGa1−xAs quantum wires. To overcome Kohn’s theorem we have in particular prepared double-layered wires and studied the acoustic magnetoplasmon branch. We find oscillations in the magnetic-field dispersion of the acoustic plasmon which are traced back to the self-consistently screened density profile in its dependence on the magnetic depopulation of the one-dimensional subbands.

Skipping Orbit Electron Motion in GaAs–AlGaAs Quantum Wires Detected by Raman Spectroscopy

We have investigated the elementary electronic excitations of the quasi-one-dimensional (1D) magnetoplasma in GaAs-AlGaAs quantum wires by resonant inelastic light scattering. In narrow quantum wire samples we observe the 1D intrasubband plasmon if a wave vector is transferred parallel to the wire direction. This 1D plasmon shows a negative dispersion with magnetic field, which arises from skipping orbit motion of the individual electrons at the edges of the wires. We find evidence for a coupling between adjacent wires in these samples with relatively small periods. Furthermore, we demonstrate theoretically and experimentally that in Raman experiments on confined magnetoplasmons in quantum wire structures with parabolic confinement the generalized Kohn theorem can be broken by using wave vector transfers q > 0.