Magnetophotoluminescence of negatively charged excitons in narrow quantum wells

We present the results of photoluminescence experiments on the negatively charged exciton X- in GaAs/AlxGa1-xAs quantum wells (QW) in high magnetic fields (≤50 T). Three different QW widths are used here: 100, 120, and 150 Å. All optically allowed transitions of X- are observed, enabling us to experimentally verify its energy-level diagram. All samples behave consistently with this diagram. We have determined the binding energy Eb of the singlet and triplet state of X- between 23 and 50 T for the 120 and 150 Å QW, while only the triplet Eb is observed for the 100 Å QW. A detailed comparison with recent theoretical calculations shows an agreement for all samples across this entire field range

Binding Energy of Charged Excitons in ZnSe-based Quantum Wells

Excitons and charged excitons (trions) are investigated in ZnSe-based quantum well structures with (Zn,Be,Mg)Se and (Zn,Mg)(S,Se) barriers by means of magneto-optical spectroscopy. Binding energies of negatively () and positively (X+) charged excitons are measured as functions of quantum well width, free carrier density and in external magnetic fields up to 47 T. The binding energy of shows a strong increase from 1.4 to 8.9 meV with decreasing quantum well width from 190 to 29 A. The binding energies of X+ are about 25% smaller than the binding energy in the same structures. The magnetic field behavior of and X+ binding energies differ qualitatively. With growing magnetic field strength, increases its binding energy by 35-150%, while for X+ it decreases by 25%. Zeeman spin splittings and oscillator strengths of excitons and trions are measured and discussed

Magnetic field dependence of the energy of negatively charged excitons in semiconductor quantum wells

A variational calculation of the spin-singlet and spin-triplet state of a negatively charged exciton (trion) confined to a single quantum well and in the presence of a perpendicular magnetic field is presented. We calculated the probability density and the pair correlation function of the singlet and triplet trion states. The dependence of the energy levels and of the binding energy on the well width and on the magnetic field strength was investigated. We compared our results with the available experimental data on GaAs/AlGaAs quantum wells and find that in the low magnetic field region (B<18 T) the observed transition are those of the singlet and the dark triplet trion (with angular momentum $L_z=-1$), while for high magnetic fields (B>25 T) the dark trion becomes optically inactive and possibly a transition to a bright triplet trion (angular momentum $L_z=0$) state is observed.Comment: 9 pages, 10 figures submitted to Phys. Rev.

A concise guide to choosing suitable gene expression systems for recombinant protein production

This overview guides both novices and experienced researchers facing challenging targets to select the most appropriate gene expression system for producing a particular protein. By answering four key questions, readers can determine the most suitable gene expression system following a decision scheme. This guide addresses the most commonly used and accessible systems and provides brief descriptions of the main gene expression systems' key characteristics to assist decision making. Additionally, information has been included for selected less frequently used "exotic" gene expression systems

Energy level diagram of X- in high magnetic fields

The photoluminescence energy of the negatively charged excitons (X-) in a 100 Å GaAs/AlGaAs quantum well (QW) using magnetic fields upto 50 T was analysed. The QW structures were grown by molecular beam epitaxy. It was found that all possible transitions of the singlet and triplet state of the X- can be determined and the energy level diagram of X- can be constructed

Proceedings of the 6th international conference of applied operational research

Operational Research is an important scientific discipline with many new theoretical developments and practical applications. The International Conference on Applied Operational Research (ICAOR) is an annual forum bringing together academics and practitioners from around the world to discuss the most recent developments in operational research and management science (OR/MS). The conference covers all aspects of our subject, but with a particular emphasis on applications. This year, the sixth event in our planned series of conferences – ICAOR 2014 takes place in the city of Vancouver, Canada. We received quality submissions from approximately 21 countries around the world and finally could accept 28 papers for presentation at the conference and publication in these proceedings. The papers that appear in this volume were carefully and thoroughly refereed. Our sincere thanks go to the members of the scientific programme committee who gave a significant amount of their valuable time to this task. We are also very grateful to all those who have helped in organising the conference. We are sure that their contributions will add significantly to the success of the conference. We very much hope that you will enjoy the conference programme and the planned social events. We wish you all a very pleasant stay in Vancouver and trust that you will find the conference to be of value and leave us having made many new friends