7 research outputs found
Electron-electron interactions in antidot-based Aharonov-Bohm interferometers
We present a microscopic picture of quantum transport in quantum antidots in
the quantum Hall regime taking electron interactions into account. We discuss
the edge state structure, energy level evolution, charge quantization and
linear-response conductance as the magnetic field or gate voltage is varied.
Particular attention is given to the conductance oscillations due to
Aharonov-Bohm interference and their unexpected periodicity. To explain the
latter we propose the mechanisms of scattering by point defects and Coulomb
blockade tunneling. They are supported by self-consistent calculations in the
Hartree approximation, which indicate pinning and correlation of the
single-particle states at the Fermi energy as well as charge oscillation when
antidot-bound states depopulate. We have also found interesting phenomena of
anti-resonance reflection of the Fano type.Comment: 12 pages, 8 figure
Electron interactions in an antidot in the integer quantum Hall regime
A quantum antidot, a submicron depletion region in a two-dimensional electron
system, has been actively studied in the past two decades, providing a powerful
tool for understanding quantum Hall systems. In a perpendicular magnetic field,
electrons form bound states around the antidot. Aharonov-Bohm resonances
through such bound states have been experimentally studied, showing interesting
phenomena such as Coulomb charging, h/2e oscillations, spectator modes,
signatures of electron interactions in the line shape, Kondo effect, etc. None
of them can be explained by a simple noninteracting electron approach.
Theoretical models for the above observations have been developed recently,
such as a capacitive-interaction model for explaining the h/2e oscillations and
the Kondo effect, numerical prediction of a hole maximum-density-droplet
antidot ground state, and spin density-functional theory for investigating the
compressibility of antidot edges. In this review, we summarize such
experimental and theoretical works on electron interactions in antidots.Comment: 73 pages, 28 figures, to be published in Physics Reports. The
resolution of some figures is reduced in this uploa
Recommended from our members
Investigating electron transport in chemical vapor deposition graphene nanostructures
This thesis investigates electron transport properties in chemical vapor deposition (CVD) graphene-related nanostructures. There are many potential electronic and optoelectronic
applications envisioned for graphene, due to its two-dimensional character and exceptional
properties. However, the lack of scalability of exfoliated graphene and the high cost of
epitaxial graphene on silicon carbide remain the major obstacles for further commercialization
of graphene devices. Different approaches to solve this problem have been proposed for
different applications and graphene grown by CVD stands out as a useful alternative and
proves to be one of the viable routes towards scalable high quality electronics.
This thesis presents a study of scalable nanostructured devices based on CVD graphene,
with the purpose of understanding the quantum physics of electron transport and demonstrating
the potential for nano-electronic applications. First, this thesis demonstrates a scalable
approach towards encapsulating and passivating high quality CVD graphene field effect
transistors (FETs), and electron scattering processes are explored by studying electrical
characterisation and magnetotransport phenomena in encapsulated CVD AB stack and large
twist angle (30◦) bilayer graphene FETs, as well as monolayer graphene FETs for reference.
The result has significant impact on the widespread implementation of graphene for its
scalable device applications. Second, in order to enhance spin-orbit coupling (SOC) in
graphene for spin transport study and spintronics applications, a graphene - transition metal
dichalcogenide (TMD) heterostructure is investigated. Phase coherence length is reduced
in the heterostructure and a special transition from weak localization (WL) to weak antilocalization
(WAL) is found around a certain carrier concentration due to surface roughness
induced patches. This result provides insight into fabrication and operation of scalable
graphene spintronic devices. Moreover, to further elucidate single-electron behaviours as
well as solve the lack of bandgap issues, graphene is studied by being patterned into various
quantum dot structures, such as nanoribbon multiple quantum dots, quantum Hall antidots,
and double quantum dots (DQDs). The presence of multiple quantum dots in series is exhibited
in a bilayer SiC epitaxial graphene nanoribbon, due to the interplay between disorder and
quantum confinement. As an alternative to etched quantum dots in graphene, antidots in the
quantum Hall regime can take advantage of Landau gaps in graphene and are explored via
magnetotransport measurements at millikelvin temperature. Single-electron behaviors such
as Aharonov-Bohm effect and Coulomb blockade effect are observed, whereas signatures of
the effective antidots proved elusive, probably due to the disorder-broadening of the Landau
levels. Finally, for the purpose of fast readout of charge and spin states, radio-frequency (RF)
reflectometry technique is developed in GaAs antidots and graphene double quantum dots,
corresponding to capacitive and resistive couplings to the devices respectively. This attempt
paves a way for characterizing the time scale of the charge transfer and spin dephasing in
graphene nanodevices. All the quantum dots studies in a scalable style lay the foundation for
further quantum metrology and quantum computation applications.
The research in this thesis enable us to better understand the quantum physics in CVD
graphene, and the fabrication and operature of CVD graphene nanostructures are highly
promising for future electronics
Superconductors at the Nanoscale
By covering theory, design, and fabrication of nanostructured superconducting materials, this monograph is an invaluable resource for research and development. Examples are energy saving solutions, healthcare, and communication technologies. Key ingredients are nanopatterned materials which help to improve the superconducting critical parameters and performance of superconducting devices, and lead to novel functionalities. Contents Tutorial on nanostructured superconductors Imaging vortices in superconductors: from the atomic scale to macroscopic distances Probing vortex dynamics on a single vortex level by scanning ac-susceptibility microscopy STM studies of vortex cores in strongly confined nanoscale superconductors Type-1.5 superconductivity Direct visualization of vortex patterns in superconductors with competing vortex-vortex interactions Vortex dynamics in nanofabricated chemical solution deposition high-temperature superconducting films Artificial pinning sites and their applications Vortices at microwave frequencies Physics and operation of superconducting single-photon devices Josephson and charging effect in mesoscopic superconducting devices NanoSQUIDs: Basics & recent advances intrinsic Josephson junction stacks as emitters of terahertz radiation| Interference phenomena in superconductor-ferromagnet hybrids Spin-orbit interactions, spin currents, and magnetization dynamics in superconductor/ferromagnet hybrids Superconductor/ferromagnet hybrid
NASA university program management information system, FY 1994
The University Program report, Fiscal Year 1994, provides current information and related statistics for 7841 grants/contracts/cooperative agreements active during the reporting period. NASA field centers and certain Headquarters program offices provide funds for those activities in universities which contribute to the mission needs of that particular NASA element. This annual report is one means of documenting the NASA-university relationship, frequently denoted, collectively, as NASA's University Program