Patrik Brusheim

Fano effect in a quantum-ring–quantum-dot system with tunable coupling

Transport measurements are presented on a quantum ring that is tunnel-coupled to a quantum dot. When the dot is in the Coulomb blockade regime, but strongly coupled to the open ring, Fano line shapes are observed in the current through the ring, when the electron number in the dot changes by 1. The symmetry of the Fano resonances is found to depend on the magnetic flux penetrating the area of the ring and on the strength of the ring-dot coupling. At temperatures above T=0.65 K the Fano effect disappears, while the Aharonov-Bohm interference in the ring persists up to T=4.2 K. Good agreement is found between these experimental observations and a single-channel scattering matrix model including decoherence in the dot.

Frequency mixing and phase detection functionalities of three-terminal ballistic junctions

Three-terminal ballistic junctions (TBJs) are fabricated from a high-mobility InP/In0.75Ga0.25As heterostructure by electron-beam lithography. The voltage output from the central branch is measured as a function of the voltages applied to the left and right branches of the TBJs. The measurements show that the TBJs possess an intrinsic nonlinearity. Based on this nonlinearity, a novel room-temperature functional frequency mixer and phase detector are realized. The TBJ frequency mixer and phase detector are expected to have advantages over traditional circuits in terms of simple structure, small size and high speed, and can be used as a new type of building block in nanoelectronics.

Spin-3/2 physics of semiconductor hole nanowires: Valence-band mixing and tunable interplay between bulk-material and orbital bound-state spin splittings

We present a detailed theoretical study of the electronic spectrum and Zeeman splitting in hole quantum wires. The spin-3/2 character of the topmost bulk-valence-band states results in a strong variation in subband-edge g factors between different subbands. We elucidate the interplay between quantum confinement and heavy-hole-light-hole mixing and identify a certain robustness displayed by low-lying hole-wire subband edges with respect to changes in the shape or strength of the wire potential. The ability to address individual subband edges in, e.g., transport or optical experiments enables the study of hole states with nonstandard spin polarization, which do not exist in spin-3/2 systems. Changing the aspect ratio of hole wires with rectangular cross section turns out to strongly affect the g factor of subband edges, providing an opportunity for versatile in situ tuning of hole-spin properties with possible application in spintronics. The relative importance of cubic crystal symmetry is discussed, as well as the spin splitting away from zone-center subband edges. (Less)

Spin Hall effect and zitterbewegung in an electron waveguide

We study spin-resolved probability distributions for electrons in a multichannel waveguide in the presence of a spin-orbit interaction. For a spin-polarized electron injection, a zitterbewegung pattern is predicted in the probability distribution of electrons in the waveguide. For a spin-unpolarized injection, the spin-resolved electron probability in the waveguide shows spin accumulations. In addition to the spin Hall phenomenon-namely, accumulations of opposite spins at the lateral edges of the waveguide-we predict the existence of a regular stripe pattern of spin accumulations in the internal region of the waveguide. We show that the predicted zitterbewegung and spin Hall effect stem from the same mechanism and are formed from coherent states of electrons in the waveguide. (Less)

Lande-like formula for the g factors of hole-nanowire subband edges

We have analyzed theoretically the Zeeman splitting of hole-quantum-wire subband edges. As is typical for any bound state, their g factor depends on both an intrinsic g factor of the material and an additional contribution arising from a finite bound-state orbital angular momentum. We discuss the quantum-confinement-induced interplay between bulk-material and orbital effects, which is nontrivial due to the presence of strong spin-orbit coupling. A compact analytical formula is provided that elucidates this interplay and can be useful for predicting Zeeman splitting in generic hole-wire geometries.

Novel room-temperature functional analogue and digital nanoelectronic circuits based on three-terminal ballistic junctions and planar quantum-wire transistors

Three-Terminal ballistic junctions (TBJs) and planar quantum-wire transistors (QWTs) are emerging nanoelectronic devices with various novel electrical properties. In this work, we realize novel nanoelectronic analogue and digital circuits with TBJs and planar QWTs made on In0.75Ga0.25As/InP two-dimensional electron gas (2DEG) material. First we show that a single TBJ can work as a frequency mixer or a phase detector. Second, we fabricate an integrated nanostructure containing two planar QWTs, which can be used as an RS flip-flop element. Third, we make a nanoelectronic circuit by the integration of two TBJs and two planar QWTs. This circuit shows the RS flip-flop functionalities with much larger noise margins in both high and low level inputs. All measurements in this work are done at room temperature.

Novel Nanoelectronic Device Applications Based on the Nonlinearity of Three‐Terminal Ballistic Junctions

Nanometer‐scale electron devices containing three‐terminal ballistic junctions are fabricated by electron‐beam lithography on InP/InGaAs two‐dimensional electron gas materials. Based on the intrinsic nonlinearity of the devices, frequency mixer, phase detector and RS flip‐flop memory functioning at room temperature are successfully achieved. The devices have simple structure layout and small size, and are expected to function at high speed.

Spin transport and spin Hall effect in J = 3 / 2 semiconductor systems

We study hole spin transport in semiconductor systems with total angular momentum J = 3/2. By deriving an expression for the polarisation vector we show that the in-plane polarisation vanishes whenever only heavy hole channels are open in the leads. We further derive a set of constraints on the spin transport through a symmetry analysis and study the hole spin Hall effect in the presence of randomly distributed scatterers.