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This work is dedicated to electron transport in atomically thin crystals. We explore hydrodynamic effects in the electron liquid of graphene and perform a comprehensive study of electronic and optical properties of a novel 2D semiconductor - indium selenide(InSe). Graphene hosts a high quality electron system with weak phonon coupling such that electron-electron scattering can be the dominant process responsible for the establishment of local equilibrium of the electronic system above liquid nitrogen temperatures. Under these conditions, charge carriers are expected to behave as a viscous fluid with a hydrodynamic behaviour similar to classical gases or liquids. In this thesis, we aimed to reveal this hydrodynamic behaviour of the electron fluid by studying transport properties of high-quality graphene devices. To amplify the hydrodynamic effects, we used a special measurement geometry in which the current was injected into the graphene channel and the voltage was measured at the contact nearest to the injector. In this geometry we detected a negative signal which is developed as a result of the viscous drag between adjacent fluid layers, accompanied by the formation of current vortices. The magnitude of the signal allowed us to perform the first measurement of electron viscosity. In order to understand how an electron liquid enters the hydrodynamic regime we studied electron transport in graphene point contacts. We observed a drop in the point contact resistance upon increasing temperature. This drop was attributed to the interaction-induced lubrication of the point contact boundaries that was found to be strong enough to prevent momentum relaxation of charge carriers. The viscosity of the electron fluid was measured over a wide range of temperatures and at different carrier densities. Experimental data was found to be in good agreement with many-body calculations. In this work we also studied transport properties of two-dimensional InSe. We observed high electron mobility transport, quantum oscillations and a fully developed quantum Hall effect. In optical studies, we revealed that due to the crystal symmetry a monolayer InSe features suppressed recombination of electron-hole pairs.

A surface acoustic wave (SAW) is a combination of a mechanical wave and a potential wave propagating on the surface of a piezoelectric substrate at the speed of sound. Such waves are widely applied in not only the communication industry, but also in quantum physics research, such as nanoelectronics, spintronics, quantum optics, and even quantum information processing. Here, I focus on low-dimensional electron transport and SAWs in GaAs and ZnO semiconductor heterostructures. The ability to pattern quantum nanostructures using gates has stimulated intense interest in research into mesoscopic physics. We have performed a series of simulations of gate structures, and having with the optimised boundary conditions and we find them to match experimental results, such as the pinch-off voltage of one-dimensional channels and SAW charge transport in induced n-i-n and n-i-p junctions. Using the improved boundary conditions, it is straightforward to model quantum devices quite accurately using standard software. With the calculated potential, we have modelled the process how a dynamic quantum dot is driven by a SAW and have analysed error mechanisms in SAW-driven quantisation (I=Nef, where N is the number of electrons in each SAW minimum, and f is the SAW resonant frequency). From energy spectroscopy measurements, we probe the electron energy inside a SAW-driven dynamic quantum dot and find that the small addition energy, which is around 3meV, is the main limitation for the SAW quantisation. To increase the confinement of SAW-driven quantum dots, we deposit a thin ZnO film, with a better piezoelectric coupling than GaAs, on a GaAs/AlGaAs heterostructure using high-target-utilisation sputtering (an Al2O3 buffer layer is deposited to protect the 2DEG during sputtering). With the ZnO, the SAW amplitude is greatly improved to 100 meV and the RF power required for pumping electrons using a SAW is greatly reduced. Finally, we have studied low-dimensional electron transport in a MgZnO/ZnO heterostructure. We have developed a technique for patterning gates using a parylene insulator, and used these to create one-dimensional quantum wires and observe electron ballistic transport with conductance quantised in units of 2e2/h The increasing electron effective mass as the 1D electron density decreases indicate that the electron-electron interaction in this MgZnO/ZnO heterostructure is strong. Because of these strong interactions, the 0.7 anomaly is observed just below each quantised plateau, and are much stronger than in GaAs quantum wires. Furthermore, we have also calculated the SAW-modulated spontaneous and piezoelectric polarisation in the ZnO heterostructure, and have observed a sign of this SAW-modulation in 2DEG density, which is different from the classical SAW-pumping mechanism. Our results show that a ZnO heterostructure should provide a good alternative to conventional III-V semiconductors for spintronics and quantum computing as they have less nuclear spins. This paves the way for the development of qubits benefiting from the low scattering of an undoped heterostructure together with potentially long spin lifetimes.

DNA molecules possess high density genetic information in living beings, as well as selfassembly and self-recognition properties that make them excellent candidates for many scientific areas, from medicine to nanotechnology. The process of electron transport through DNA is important because DNA repair occurs spontaneously via the process that restores mismatches and lesions, and furthermore, DNA-based molecular electronics in nano-bioelectronics can be possible through the process. In this thesis, we study theoretically the transport properties through a one-dimensional one-channel DNA model, a quasi-one-dimensional one-channel DNA model, and a two-dimensional four-channel DNA model by using the Tight-Binding Hamiltonian method. We show graphical outputs of the transmission, overall contour plots of transmission, localization lengths, the Lyapunov exponent, and current-voltage characteristics as a function of incoming electron energy and magnetic flux which are obtained using Mathematica run on the CSH Beowulf Cluster. Our results show that the semiconductor behavior can be observed in the I-V characteristics. The current through a quasi-one-dimensional one-channel DNA model starts to flow after the breakdown voltage and remains constant after threshold voltage. The variations of the temperature make the fluctuations of the system. As the temperature increases, the sharp transmission resonances are smeared out and the localization lengths are also decreased. Due to a magnetic field penetrating at the center of the two-dimensional DNA model, the Aharonov- Bohm (AB) oscillations can be observed. / Sequence dependent electron transport through a one-dimensional, one-channel DNA model -- Backbone-induced effects on charge transport through a quasi one-dimensional DNA molecule -- Temperature and magnetic fields effects on the electron transport through two-dimensional and four-channel DNA model.

Thesis (Ph.D.), Memorial University of Newfoundland, 2000. / Bibliography: leaves 178-185.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 130-142).

Electron heat transport at the scale of electron gyroradius are investigated via numerical simulation of a fluid model and a role of E x B shear flow with intermediate E x B shearing rate is explored in Euler's equation. The anomalous transport, enhanced transport due to turbulent electro-magnetic fields caused by plasma instabilities, has been a focus of the inter-national fusion research communities. Among the instabilities, the drift-type instabilities from the pressure-gradient universal in magnetic fusion devicesare considered responsible for the anomalous transport. In the current status of wide use of wave heating on electrons and subsequent high core electron temperature, the turbulent heat loss through electrons has one of the most important science element in preventing the large fusion tokamaks from reaching breakeven in the past decade. The Electron Temperature Gradient fluid model consists of electrostatic potential, toroidal magnetic flux function and electron temperature (or pressure) describing electron drift waves. The fluid model proves to be highly useful to electron heat flux analysis in fusion machines. We analyze the discharges in National Spherical Tokamak eXperiment(NSTX) and Tokamak Configuration Variable (TCV) and found that the electron thermal diffusivities can be explained in terms of the mixing length argument based on electron gyroradius, linear theory and our nonlinear fluid simulation. The nonlinear fluid model predicts reasonable heat flux observed in the experiments. Based on the analysis, we investigate the dependences of the dynamics on the ratio of electron and ion temperature T[subscript e]/T[subscript i] and plasma beta [beta subscript e-]. The nonlinear dynamics such as saturation mechanism of the ETG turbulence and the electromagnetic dynamics in terms of micro-tearing at the scale of electron gyroradius are discussed briegly. In most of plasma confinement devices, the equilibrium radial electric field exists and the turbulence-generated electric field is observed. The coherent structure, called as zonal flow, has been know to be effective to suppress the micro-turbulence. But at intermediate E x B shear, where the vortex eddy turn-over time is comparable to E x B shearing rate, the suppression is weak and the flow shear can leads to vortex amplification through interaction of nonlinear dynamics and shear flow. / text

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In this work, we investigate effects of strong correlation to quantum transport from atomic first principles. In order to accomplish this task, we use a well established state-of-the-art formalism of quantum transport where density functional theory (DFT) is carried out within the Keldysh non-equilibrium Green's functions (NEGF). To deal with certain strong correlation phenomenon, we integrated an local density approximation plus Hubbard U (LDA+U) exchange-correlation potential into the existing NEGF-DFT formalism. The LDA+U potential correctly accounts for the electronic structure of correlated material. We will present the theory and numerical implementation associated with the NEGF-DFT-(LDA+U) in detail. Extensive tests on the well known correlated material FeO crystal have been carried out and results compared with previous literature as well as to experimental data. / We then apply our NEGF-DFT-(LDA+U) technique to investigate transport physics of spin resolved tunnelling in Fe/MgO/Fe magnetic tunnel junctions (MTJ). We found that interfacial oxygen atoms are enough to localise the 3d electrons of infacial Fe atoms due to strong correlation. This surprising result substantially changes quantum transport properties of the MTJ, in particular it reduces magnetic resistance ratio by about 33%. This strongly correlated physics is absent if the conventional local spin density approximation (LSDA) is used in the NEGF-DFT analysis. Results of LSDA and LDA+ U exchange-correlation potential will be compared. Furthermore, through investigating contributions to scattering states by various atomic orbitals, we clearly identify the reason why LDA+U changes quantum transport in both quantitative and qualitative ways. Finally, we believe this strongly correlated physics should be general in other MTJs involving different oxides.