High-sensitive superconducting magnetometry on a two-dimensional electron gas up to 10 Tesla

We report on new magnetization studies on a two-dimensional electron system (2DES) revealing spin splitting of the Landau levels. For this, we have built a high-sensitive susceptometer consisting of a low-noise thin-film dc superconducting quantum interference device (SQUID) with a multiturn input coil and a wire-wound first-order gradiometer. The system noise level is only 40×10 −6 Φ 0 /√ (Hz) down to a frequency of a few Hz in unshielded environment. In background fields up to 10 T, the system exhibits significant low-frequency noise. At frequencies above 1 kHz, however, the SQUID sensitivity is barely affected and we have reached a value of about 10 −14 J/T at 1 T and better than 10 −13 J/T at 10 T. With this, we have studied the de Haas–van Alphen effect for a tunable 2DES starting from zero carrier density

Magneto-Optical Investigation of Excitons in Narrow GaAs-AlGaAs Quantum Wires

We present a method for the preparation of GaAs-AlGaAs quantum wire arrays starting from holographically prepared masks. The combination of reactive ion etching and stepwise wet-chemical etching allows us to produce narrow quantum wires. We achieved wire widths down to 40 nm. The diamagnetic shift of the magnetoexcitons in our samples shows clear evidence of enhanced Coulomb interaction between photocreated electrons and holes due to the lateral confinement. A decrease of the lateral extension of the excitonic wave function from 10.6 nm in the 2D reference sample to 7.4 nm in the 40 nm wide quantum wires is deduced from the data

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

We investigate electronic excitations in GaAs–AlGaAs quantum dots by means of resonant inelastic light scattering in the presence of an external magnetic field Image . At magnetic field Image , we observe a series of discrete electronic excitations, namely, charge-density excitations (CDEImage ) and spin-density excitations (SDEImage ), in one and the same quantum dot sample. We find at finite magnetic field, additionally to the well-known splitting of the CDEImage 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