A Hanbury Brown and Twiss experiment for a beam of electrons has been realized in a two-dimensional electron gas in the quantum Hall regime. A metallic split gate serves as a tunable beam splitter to partition the incident beam into transmitted and reflected partial beams. In the nonequilibrium case the fluctuations in the partial beams are shown to be fully anticorrelated, demonstrating that fermions exclude each other. In equilibrium, the cross-correlation of current fluctuations at two different contacts is also found to be negative and nonzero, provided that a direct transmission exists between the contacts.

We study the effect of the edge disorder on the conductance of the graphene nanoribbons (GNRs). We find that already very modest edge disorder is sufficient to induce the conduction energy gap in the otherwise metallic GNRs and to lift any difference in the conductance between nanoribbons of different edge geometry. We relate the formation of the conduction gap to the pronounced edge-disorder-induced Anderson-type localization which leads to the strongly enhanced density of states at the edges, formation of surfacelike states, and to blocking of conductive paths through the ribbons.

The surface of shallow Ga[Al]As heterostructures is locally oxidized with an atomic force microscope. The electron gas underneath the oxide is depleted. We demonstrate experimentally that these depleted regions of the two-dimensional electron gas can be made highly resistive at liquid nitrogen temperatures. Thus, local anodic oxidation of high electron mobility transistors with an atomic force microscope provides a novel method to define nanostructures and in-plane gates. Two examples, namely antidots and quantum point contacts as in-plane gate transistors have been fabricated and their performance at low temperatures is discussed.

Low-temperature conductance measurements have been performed upon a parallel quantum-dot configuration defined in the two-dimensional electron gas of a GaAs-${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructure. The observed Coulomb-blockade oscillations of the conducting dot exhibit pronounced periodic shifts as a consequence of the tunable coupling to the nonconducting dot. We show that the transport is essentially determined by the interdot capacitance and that the addition of a single electron to the nonconducting dot can switch the device conductance from a maximum to a Coulomb-blockade minimum.

We investigate the crossover between weak localization and weak antilocalization in InAs nanowires of different diameters (75 nm-140 nm-217 nm). For a magnetic field applied perpendicularly to the nanowire axis, we extract the spin orbit and coherence lengths using a quasi-one-dimensional model of the conductance. We find a spin-orbit length inversely proportional to the width of the nanowire. When a parallel magnetic field is applied, we observe that the weak-antilocalization contribution is less affected by the magnetic field than in the perpendicular case.