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We demonstrate the presence of a resonant interaction between a pair of coupled quantum wires, which are realized in the ultra-high mobility two-dimensional electron gas of a GaAs/AlGaAs quantum well. Measuring the conductance of one wire, as the width of the other is varied, we observe a resonant peak in its conductance that is correlated with the point at which the swept wire pinches off. We discuss this behaviour in terms of recent theoretical predictions concerning local spin-moment formation in quantum wires.

Cobalt oxide films are of technological interest as magnetic substrates that may support the direct growth of graphene, for use in various spintronic applications. In this work, we demonstrate the controlled growth of both Co_3O_4(111) and CoO(111) on Ru(0001) substrates. The growth is performed by Co molecular beam epitaxy, at a temperature of 500 K and in an O_2 partial pressure of 10^(−4) Torr for Co_3O_4(111), and 7.5 × 10^(−7) Torr for CoO(111). The films are distinguished by their dissimilar Co 2p x-ray photoemission (XPS) spectra, while XPS-derived O/Co stoichiometric ratios are 1.33 for Co3O4(111) and 1.1 for CoO(111). Electron energy loss (EELS) spectra for Co_3O_4(111) indicate interband transitions at ~2.1 and 3.0 eV, while only a single interband transition near 2.0 eV is observed for CoO(111). Low energy electron diffraction (LEED) data for Co_3O_4(111) indicate twinning during growth, in contrast to the LEED data for CoO(111). For Co_3O_4(111) films of less than 20 A average thickness, however, XPS, LEED and EELS data are similar to those of CoO(111). XPS data indicate that both Co oxide phases are hydroxylated at all thicknesses. The two phases are moreover found to be thermally stable to at least 900 K in UHV, while ex situ atomic force microscopy measurements of Co_3O_4(111)/Ru(0001) indicate an average surface roughness below 1 nm. Electrical measurements indicate that Co_3O_4(111)/Ru(0001) films exhibit dielectric breakdown at threshold voltages of ~1 MV cm^(−1). Collectively, these data show that the growth procedures yield Co_3O_4(111) films with topographical and electrical characteristics that are suitable for a variety of advanced device applications.

We demonstrate that low-temperature illumination of a GaAs/AlGaAs Hall bar, partially covered by a split metal gate structure, results in the formation of a shallow barrier across the entire device, even in the point contact openings not directly covered by the gates. The minimum carrier density inhomogeneity is determined from the position of the anomalous Hall steps, which are observed even at zero gate voltage as a result of barrier formation. Our results suggest a substantial contribution to the carrier density inhomogeneity, implying that low-temperature illumination may considerably increase disorder in split gate nanostructures.

We discuss the application of a novel class of device, the magneto-electric magnetic tunnel junction (ME-MTJ) to realize a variety of computational functions, including majority logic and the XNOR/XOR gate. We also develop a compact model to describe the operation of these devices, which function by utilizing the phenomenon of 'voltage-controlled magnetism' to switch the operational state of MTJs. The model breaks down the switching process into three key stages of operation: electrical-to-magnetic conversion, magnetization transfer, and final-state readout. Estimates for the switching energy and delay of these devices, obtained from this compact model, reveal significant improvements in both of these parameters when compared to conventional MTJs switched by spin-transfer-torque. In fact, the capacity to use the ME-MTJ to implement complex logical operations within a single device allows its energy costs to even approach those of low-power CMOS. The added benefits of non-volatility and compact circuit footprint, combined with their potential for heterogeneous integration with CMOS, make the ME devices of considerable interest for post-CMOS technology.

We have studied the low-temperature magnetotransport in quantum dots and wires. Using the correlation function and electron focusing methods, we observed evidence for the presence of a stabilized orbit in the dot and wire. We have also studied a geometry-induced fractal behaviour of the magnetotransport in the quantum dot and wire, which confirms the regularity of the dominant orbits.

The conductance of open quantum dot devices is shown to reveal a series of strikingly periodic oscillations as the negative bias applied to their defining gates is varied at zero magnetic field. These surprisingly regular oscillations persist with unaltered characteristics over a wide range of gate voltages, suggesting that the intrinsic transport properties of these devices are dominated by the selective excitation of a small number of stable orbits.

Quantum dots provide a natural system in which to study both quantum and classical features of transport. As a closed testbed, they provide a natural system with a very rich set of eigenstates. When coupled to the environment through a pair of quantum point contacts, each of which passes several modes, the original quantum environment evolves into a set of decoherent and coherent states, which classically would compose a mixed phase space. The manner of this breakup is governed strongly by Zurek's decoherence theory, and the remaining coherent states possess all the properties of his pointer states. These states are naturally studied via traditional magnetotransport at low temperatures. More recently, we have used scanning gate (conductance) microscopy to probe the nature of the coherent states, and have shown that families of states exist through the spectrum in a manner consistent with quantum Darwinism. In this review, we discuss the nature of the various states, how they are formed, and the signatures that appear in magnetotransport and general conductance studies.

A method for the fabrication of sub-micron width mesas of GaAs/Ga1-xAlxAs heterojunction material is presented. The technique employs optical lithography and wet etching and is considered to cause minimal damage to the material. The exceptionally smooth etch surfaces obtained make the structures highly suitable for the study of quasi-one-dimensional transport phenomena.