Abstract:
There currently is a large effort to explore spin-orbit effects in semiconductor structures with the ultimate goal of manipulating electron spins with gates. A search for materials with large spin-orbit coupling is therefore important. We report results of a study of spin-orbit effects in a strained InGaAs/InP quantum well. The spin-orbit relaxation time, determined from the weak antilocalization effect, was found to depend non-monotonically on gate voltage. The spin orbit scattering rate had a maximum value of $5\times 10^{10}s^{-1}$ at an electron density of $n=3\times 10^{15} m^{-2}$. The scattering rate decreased from this for both increasing and decreasing densities. The smallest measured value was approximately $10^9 s^{-1}$ at an electron concentration of $n=6\times 10^{15} m^{-2}$. This behavior could not be explained by either the Rashba nor the bulk Dresselhaus mechanisms but is attributed to asymmetry or strain effects at dissimilar quantum well interfaces.

Abstract:
We have performed single electron spectroscopy experiments on single lateral quantum dots. We demonstrate that the lateral nature of the tunneling as well as the properties of the 2DEG leads can be used to extract new information in the 'spin-flip' regime. Calculations confirm that one needs to go beyond the Hartree-Fock approximation and include correlation effects to explain the experimental observations. The results are found to be consistent with the presence of spin depolarization events at the 'spin-flips'.

Abstract:
Magnetoresistance results are presented for p-SiGe samples on the metallic side of the B=0 metal-insulator transition. It was possible to separate the weak localisation and Zeeman interaction effects but the results could not be explained quantitatively within the framework of standard theories for quantum corrections of a weakly interacting 2-dimensional system. Analysis using a theory for interaction corrections at intermediate temperatures, recently proposed by Zala, Narozhny and Aleiner, provided values of the Fermi liquid parameter $F_0^{\sigma}$ of order -0.5. Similar values also explain the linear increase of resistance with temperature characteristic of the metallic phase. e

Abstract:
Magnetoresistance results are presented for p-SiGe samples on the metallic side of the B=0 metal-insulator transition. The results cannot be understood within the framework of standard theories for quantum corrections of a weakly interacting 2- dimensional system. In particular no logarithmic dependence on temperature is observed, at low fields, in either the longitudinal or Hall resistivities despite evidence in the magnetoresistance of weak localisation effects. Further, the Hall coefficient shows a strong logarithmic dependence on field. The results are better explain by renormalisation group theories and by an anomalous Hall effect associated with strong spin-orbit coupling in the presence of a background spin texture.

Abstract:
In this paper we report on a tuneable few electron lateral triple quantum dot design. The quantum dot potentials are arranged in series. The device is aimed at studies of triple quantum dot properties where knowing the exact number of electrons is important as well as quantum information applications involving electron spin qubits. We demonstrate tuning strategies for achieving required resonant conditions such as quadruple points where all three quantum dots are on resonance. We find that in such a device resonant conditions at specific configurations are accompanied by novel charge transfer behaviour.

Abstract:
We study experimentally the electron transport properties of gated quantum dots formed in InGaAs/InP and InAsP/InP quantum well structures grown by chemical-beam epitaxy. For the case of the InGaAs quantum well, quantum dots form directly underneath narrow gate electrodes due to potential fluctuations. We measure the Coulomb-blockade diamonds in the few-electron regime of a single quantum dot and observe photon-assisted tunneling peaks under microwave irradiation. A singlet-triplet transition at high magnetic field and Coulomb-blockade effects in the quantum Hall regime are also observed. For the InAsP quantum well, an incidental triple quantum dot forms also due to potential fluctuations within a single dot layout. Tunable quadruple points are observed via transport measurements.

Abstract:
This paper reports on the observation and analysis of magnetotransport phenomena in the nonlinear differential resistance $r_{xx}=dV_{xx}/dI$ of high-mobility InGaAs/InP and GaAs/AlGaAs Hall bar samples driven by direct current, $\Idc$. Specifically, it is observed that Shubnikov -de Haas (SdH) oscillations at large filling factors invert their phase at sufficiently large values of $\Idc$. This phase inversion is explained as being due to an electron heating effect. In the quantum Hall effect regime the $r_{xx}$ oscillations transform into diamond-shaped patterns with different slopes corresponding to odd and even filling factors. The diamond-shaped features at odd filling factors can be used as a probe to determine spin energy gaps. A Zero Current Anomaly (ZCA) which manifests itself as a narrow dip in the $r_{xx}(\Idc)$ characteristics at zero current, is also observed. The ZCA effect strongly depends upon temperature, vanishing above 1 K while the transport diamonds persist to higher temperatures. The transport diamonds and ZCA are fully reproduced in a higher mobility GaAs/AlGaAs Hall bar structure confirming that these phenomena reflect intrinsic properties of two-dimensional systems.

Abstract:
A few electron double electrostatic lateral quantum dot can be transformed into a few electron triple quantum dot by applying a different combination of gate voltages. Quadruple points have been achieved at which all three dots are simultaneously on resonance. At these special points in the stability diagram four occupation configurations are possible. Both charge detection and transport experiments have been performed on this device. In this short paper we present data and confirm that transport is coherent by observing a Pi phase shift in magneto-conductance oscillations as one passes through the quadruple point.

Abstract:
Conductance fluctuations have been studied in a soft wall stadium and a Sinai billiard defined by electrostatic gates on a high mobility semiconductor heterojunction. These reproducible magnetoconductance fluctuations are found to be fractal confirming recent theoretical predictions of quantum signatures in classically mixed (regular and chaotic) systems. The fractal character of the fluctuations provides direct evidence for a hierarchical phase space structure at the boundary between regular and chaotic motion.