Spectroscopy of nanoscopic semiconductor rings

Making use of self-assembly techniques, we demonstrate the realization of nanoscopic semiconductor quantum rings in which the electronic states are in the true quantum limit. We employ two complementary spectroscopic techniques to investigate both the ground states and the excitations of these rings. Applying a magnetic field perpendicular to the plane of the rings, we find that when approximately one flux quantum threads the interior of each ring, a change in the ground state from angular momentum $\ell = 0$ to $\ell = -1$ takes place. This ground state transition is revealed both by a drastic modification of the excitation spectrum and by a change in the magnetic field dispersion of the single-electron charging energy

Exploring factors associated with participation in citizen science among UK museum visitors aged 40-60: A qualitative study using the theoretical domains framework and the capability opportunity motivation-behaviour model

Citizen science has grown as a form of public engagement in science. Middle-aged citizens who are already consuming scientific information should be a potential outreach group. Behaviour change research in citizen science participation among the demographic is lacking. A total of 47 museum visitors aged 40-60 years took part in qualitative questionnaires and semi-structured interviews. Thematic analysis with the aid of theoretical domains framework and capability opportunity motivation-behaviour model revealed eight themes: (1) limited awareness of citizen science; (2) curiosity, competence and other significant characteristics and skills; (3) important beliefs about one's capability; (4) importance of clear project purpose and impacts; (5) interest, enjoyment and incentives; (6) lasting impacts of family upbringing; (7) project details that make participation easy, better project promotion; and (8) the living environment, availability of free time and money. Addressing a maximum number of these factors with behaviour change techniques can improve the likelihood of citizen science participation

Magneto-capacitance probing of the many-particle states in InAs dots

We use frequency-dependent capacitance-voltage spectroscopy to measure the tunneling probability into self-assembled InAs quantum dots. Using an in-plane magnetic field of variable strength and orientation, we are able to obtain information on the quasi-particle wave functions in momentum space for 1 to 6 electrons per dot. For the lowest two energy states, we find a good agreement with Gaussian functions for a harmonic potential. The high energy orbitals exhibit signatures of anisotropic confinement and correlation effects.Comment: 3 pages, 3 figure

Influence of carrier-carrier and carrier-phonon correlations on optical absorption and gain in quantum-dot systems

A microscopic theory is used to study the optical properties of semiconductor quantum dots. The dephasing of a coherent excitation and line-shifts of the interband transitions due to carrier-carrier Coulomb interaction and carrier-phonon interaction are determined from a quantum kinetic treatment of correlation processes. We investigate the density dependence of both mechanisms and clarify the importance of various dephasing channels involving the localized and delocalized states of the system.Comment: 12 pages, 10 figure

Quantum Jumps on a Circle

It is demonstrated that in contrast to the well-known case with a quantum particle moving freely in a real line, the wave packets corresponding to the coherent states for a free quantum particle on a circle do not spread but develop periodically in time. The discontinuous changes during the course of time in the phase representing the position of a particle can be interpreted as the quantum jumps on a circle.Comment: LaTeX, 3 PostScript figure

Excitation-induced energy shifts in the optical gain spectra of InN quantum dots

A microscopic theory for the optical absorption and gain spectra of InN quantum-dot systems is used to study the combined influence of material properties and interaction-induced effects. Atomistic tight-binding calculations for the single-particle properties of the self-assembled quantum-dot and wetting-layer system are used in conjunction with a many-body description of Coulomb interaction and carrier phonon interaction. We analyze the carrier-density and temperature dependence of strong excitation-induced energy shifts of the dipole-allowed quantum-dot transitions.(C) 2009 American Institute of Physics. (10.1063/1.3213543