Magnetotransport in a nonplanar two-dimensional electron gas

Electric field and curvature effects on relativistic Landau levels on a pseudosphere

In this paper relativistic Landau levels on a carbon pseudosphere, whose curvature is a negative constant K  =  -R ^-2, are investigated analytically in the presence of orthogonal electric and magnetic fields. It has been shown that the magnetic field tends to create bound states while the electric field tends to destroy them. Consequently there exists a critical electric field such that beyond this critical field the Landau levels collapse although negative curvature of the pseudosphere acts towards preventing the collapse of Landau levels at the critical value.

Use of quantum effects as potential qualifying metrics for "quantum grade silicon"

Across solid state quantum information, materials deficiencies limit performance through enhanced relaxation, charge defect motion or isotopic spin noise. While classical measurements of device performance provide cursory guidance, specific qualifying metrics and measurements applicable to quantum devices are needed. For quantum applications, new materials metrics, e.g., enrichment, are needed, while existing, classical metrics like mobility might be relaxed compared to conventional electronics. In this work, we examine locally grown silicon superior in enrichment, but inferior in chemical purity compared to commercial-silicon, as part of an effort to underpin the materials standards needed for quantum grade silicon and establish a standard approach for intercomparison of these materials. We use a custom, mass-selected ion beam deposition technique, which has produced isotopic enrichment levels up to 99.99998 % 28Si, to isotopically enrich 28Si, but with chemical purity > 99.97% due the MBE techniques used. From this epitaxial silicon, we fabricate top-gated Hall bar devices simultaneously on the 28Si and on the adjacent natural abundance Si substrate for intercomparison. Using standard-methods, we measure maximum mobilities of ≈ ( 1740 ± 2 ) cm 2 / ( V ⋅ s ) at an electron density of ( 2.7 × 10 12 ± 3 × 10 8 ) cm-2 and ≈ ( 6040 ± 3 ) cm 2 / ( V ⋅ s ) at an electron density of ( 1.2 × 10 12 ± 5 × 10 8 ) cm-2 at T = 1.9 K for devices fabricated on 28Si and natSi, respectively. For magnetic fields B > 2 T, both devices demonstrate well developed Shubnikov-de Haas (SdH) oscillations in the longitudinal magnetoresistance. This provides transport characteristics of isotopically enriched 28Si, and will serve as a benchmark for classical transport of 28Si at its current state, and low temperature, epitaxially grown Si for quantum devices more generally.

Electron dynamics in inhomogeneous magnetic fields

This review explores the dynamics of two-dimensional electrons in magnetic potentials that vary on scales smaller than the mean free path. The physics of microscopically inhomogeneous magnetic fields relates to important fundamental problems in the fractional quantum Hall effect, superconductivity, spintronics and graphene physics and spins out promising applications which will be described here. After introducing the initial work done on electron localization in random magnetic fields, the experimental methods for fabricating magnetic potentials are presented. Drift-diffusion phenomena are then described, which include commensurability oscillations, magnetic channelling, resistance resonance effects and magnetic dots. We then review quantum phenomena in magnetic potentials including magnetic quantum wires, magnetic minibands in superlattices, rectification by snake states, quantum tunnelling and Klein tunnelling. The third part is devoted to spintronics in inhomogeneous magnetic fields. This covers spin filtering by magnetic field gradients and circular magnetic fields, electrically induced spin resonance, spin resonance fluorescence and coherent spin manipulation.

Quantized magnetic confinement in quantum wires

Ballistic quantum wires are exposed to longitudinal profiles of perpendicular magnetic fields composed of a spike and a homogeneous part. An asymmetric magnetoconductance peak as a function of the homogeneous magnetic field is found, comprising quantized conductance steps in the interval where the homogeneous magnetic field and the magnetic barrier have identical polarities, and a characteristic shoulder with several resonances in the interval of opposite polarities. The observations are interpreted in terms of inhomogeneous diamagnetic shifts of the quantum wire modes leading to magnetic confinement.

Tunable Lyapunov exponent in inverse magnetic billiards

The stability properties of the classical trajectories of charged particles are investigated in a two-dimensional inverse magnetic domain, where the magnetic field is zero inside the domain and constant outside. As an example, we present detailed analysis for stadium-shaped domain. In the case of infinite magnetic field, the dynamics of the system is the same as in the Bunimovich billiard, i.e., ergodic and mixing. However, for weaker magnetic fields, the phase space becomes mixed and the chaotic part gradually shrinks. The numerical measurements of the Lyapunov exponent (based on the technique of Jacobi fields) and the regular-to-chaotic phase space volume ratio show that both quantities can smoothly be tuned by varying the external magnetic field. A possible experimental realization of the inverse magnetic billiard is also discussed.

Magnetic quantum dot: a magnetic transmission barrier and resonator

We study the ballistic edge-channel transport in quantum wires with a magnetic quantum dot, which is formed by two different magnetic fields B(*) and B0 inside and outside the dot, respectively. We find that the electron states located near the dot and the scattering of edge channels by the dot strongly depend on whether B(*) is parallel or antiparallel to B0. For parallel fields, two-terminal conductance as a function of channel energy is quantized except for resonances, while, for antiparallel fields, it is not quantized and all channels can be completely reflected in some energy ranges. All these features are attributed to the characteristic magnetic confinements caused by nonuniform fields.

Resistance resonance effects through magnetic edge states

We report on the magnetoresistance of a two-dimensional electron gas subjected to an abrupt magnetic field gradient arising from a ferromagnetic stripe fabricated at its surface. A sharp resistance resonance effect is observed at B(p) due to the formation of two types of magnetic edge states that drift in opposite directions perpendicular to the magnetic field gradient for B<B(p) and B>B(p). A semiclassical drift-diffusion model gives a good description of the effects of the magnetic confinement on both the diagonal and off-diagonal components of the resistivity tensor.