A. A. M. Staring

Single electron charging effects in semiconductor quantum dots

We have studied charging effects in a lateral split-gate quantum dot defined by metal gates in the two dimensional electron gas (2 DEG) of a GaAs/AlGaAs heterostructure. The gate structure allows an independent control of the conductances of the two tunnel barriers separating the quantum dot from the two 2 DEG leads, and enables us to vary the number of electrons that are localized in the dot. We have measured Coulomb oscillations in the conductance and the Coulomb staircase in current-voltage characteristics and studied their dependence on the conductances of the tunnel barriers. We show experimentally that at zero magnetic field charging effects start to affect the transport properties when both barrier conductances are smaller than the first quantized conductance value of a point contact at 2e2/h. The experiments are described by a simple model in terms of electrochemical potentials, which includes both the discreteness of the electron charge and the quantum energy states due to confinement.

Coulomb-Blockade Oscillations in the Thermopower of a Quantum Dot.

The thermopower of a quantum dot, defined in the two-dimensional electron gas in a GaAs-AlxGa1-xAs heterostructure, is investigated using a current heating technique. At lattice temperatures kBT much smaller than the charging energy e2/C, and at small heating currents, sawtoohlike thermopower oscillations are observed as a function of gate voltage, in agreement with a recent theory. In addition, a remarkable sign reversal of the amplitude of the thermopower oscillations is found in the non-linear regime at large heating currents.

Coulomb-Blockade Oscillations in Semiconductor Nanostructures

A resume is given of recent theoretical and experimental work on single-electron tunneling in the size quantized regime in semiconductor quantum dots and wires. In addition, the quantum Hall effect regime is discussed.

Coulomb-blockade oscillations in a quantum dot

Abstract Periodic oscillations as a function of gate voltage have been observed in the conductance of a quantum dot defined in a two-dimensional electron gas by three pairs of gates. They are interpreted as Coulomb-blockade oscillations. The amplitude of the oscillations can be enhanced up to e 2 / h in the quantum Hall effect regime.

Sawtooth-like thermopower oscillations of a quantum dot in the Coulomb blockade regime

Current heating is used to measure the thermopower of a quantum dot in the Coulomb blockade regime. We observe sawtooth-like oscillations as a function of gate voltage in the thermovoltage across the dot. These observations are compared with measured Coulomb blockade oscillations in the conductance, and with theory.

Quantum effects in thermal and thermo-electric transport in semiconductor nanostructures

Current heating is used to create a micron-scale hot electron reservoir in semiconductor nanostructures at low temperatures. This techniques enables the study of quantum effects in various thermo-electric transport coefficients.

Coulomb-Regulated Conductance Oscillations in a Disordered Quantum Wire

Disordered quantum wires have been defined by means of a splitgate lateral depletion technique in the two-dimensional electron gas in GaAs-AlGaAs heterostructures, the disorder being due to the incorporation of a layer of beryllium acceptors in the 2DEG. In contrast to the usual aperiodic conductance fluctuations due to quantum interference, periodic conductance oscillations are observed experimentally as a function of gate voltage (or density). No oscillations are seen in the magnetoconductance, although a strong magnetic field dramatically enhances the amplitude of the oscillations periodic in the gate voltage. The fundamentally different roles of gate voltage and magnetic field are elucidated by a theoretical study of a quantum dot separated by tunneling barriers from the leads. A formula for the periodicity of the conductance oscillations is derived which describes the regulation by the Coulomb interaction of resonant tunneling through zero-dimensional states, and which explains the suppression of the magnetoconductance oscillations observed experimentally.

1/f noise in a quasi‐one‐dimensional channel

We perform a noise‐spectroscopy study on electron transport through a narrow split‐gate GaAs/AlGaAs channel. The noise is found to be dominated by a 1/f contribution, which is interpreted to originate from time‐dependent fluctuations in the electrostatic potential in the channel due to electron trapping and detrapping processes with a broad distribution of time constants.

Coulomb-blockade oscillations in quantum wires and dots

Single electron tunneling can cause periodic oscillations to appear in the conductance as a function of gate voltage in split-gate nanostructures defined in the two-dimensional electron gas in GaAs-AlGaAs heterostructures. We review our theoretical and experimental results on these Coulomb-blockade oscillations in the resonant tunneling regime, where the transfer of single electrons proceeds through discrete energy levels.

Lateral electron transport through a quantum dot : Coulomb blockade and quantum transport

We have fabricated a versatile quantum dot device.defined in a twodimensional electron gas by three pairs of gates. In the quantum transport regime, where the entrance and exit barrier conductances were greater than 2e/h, corresponding to two quantum point contacts in series, we have observed conductance plateaux corresponding to the lowest conductance point contact, modulated, at low temperature, by a period similar to that of the conductance plateau Separation for a single quantum point contact. For the case where the conductance of both barriers was less than 2e/h, periodic oscillations have been observed äs a function of gate voltage which we interpret äs coulomb blockade oscillations. These oscillations were observed even when the electrons in the dot were poorly confmed.