Excitons and charged excitons in semiconductor quantum wells

A variational calculation of the ground-state energy of neutral excitons and of positively and negatively charged excitons (trions) confined in a single-quantum well is presented. We study the dependence of the correlation energy and of the binding energy on the well width and on the hole mass. The conditional probability distribution for positively and negatively charged excitons is obtained, providing information on the correlation and the charge distribution in the system. A comparison is made with available experimental data on trion binding energies in GaAs-, ZnSe-, and CdTe-based quantum well structures, which indicates that trions become localized with decreasing quantum well width.Comment: 9 pages, 11 figure

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.

The Late Cretaceous to recent tectonic history of the Pacific Ocean basin

A vast ocean basin has spanned the region between the Americas, Asia and Australasia for well over 100 Myr, represented today by the Pacific Ocean. Its evolution includes a number of plate fragmentation and plate capture events, such as the formation of the Vancouver, Nazca, and Cocos plates from the break-up of the Farallon plate, and the incorporation of the Bellingshausen, Kula, and Aluk (Phoenix) plates, which have been studied individually, but never been synthesised into one coherent model of ocean basin evolution. Previous regional tectonic models of the Pacific typically restrict their scope to either the North or South Pacific, and global kinematic models fail to incorporate some of the complexities in the Pacific plate evolution (e.g. the independent motion of the Bellingshausen and Aluk plates), thereby limiting their usefulness for understanding tectonic events and processes occurring in the Pacific Ocean perimeter. We derive relative plate motions (with 95% uncertainties) for the Pacific-Farallon/Vancouver, Kula-Pacific, Bellingshausen-Pacific, and early Pacific-West Antarctic spreading systems, based on recent data including marine gravity anomalies, well-constrained fracture zone traces and a large compilation of magnetic anomaly identifications. We find our well-constrained relative plate motions result in a good match to the fracture zone traces and magnetic anomaly identifications in both the North and South Pacific. In conjunction with recently published and well-constrained relative plate motions for other Pacific spreading systems (e.g. Aluk-West Antarctic, Pacific-Cocos, recent Pacific-West Antarctic spreading), we explore variations in the age of the oceanic crust, seafloor spreading rates and crustal accretion and find considerable refinements have been made in the central and southern Pacific. Asymmetries in crustal accretion within the overall Pacific basin (where both flanks of the spreading system are preserved) have typically deviated less than 5% from symmetry, and large variations in crustal accretion along the southern East Pacific Rise (i.e. Pacific-Nazca/Farallon spreading) appear to be unique to this spreading corridor. Through a relative plate motion circuit, we explore the implied convergence history along the North and South Americas, where we find that the inclusion of small tectonic plate fragments such as the Aluk plate are critical for reconciling the history of convergence with onshore geological evidence. © 2015 Elsevier B.V.Australian Research Council, M.S.I. Foundatio

The Rodriguez Triple Junction (Indian Ocean): Structure and evolution for the past one million years

The Rodriguez Triple Junction (RTJ) corresponds to the junction of the 3 Indian Ocean spreading ridges. A detailed survey of an area of 90 km by 85 km, centered at 25 degree 30 degree S and 70 degree E, allows detailed mapping (at a scale of 1/100,000) of the bathymetry (Seabeam) and the magnetic anomalies. The Southeast Indian Ridge, close to the triple junction, is a typical intermediate spreading rate ridge (2.99 cm/a half rate) trending N140 degree . The Central Indian Ridge rift valley prolongs the Southeast Indian Ridge rift valley with a slight change of orientation (12 degree ). The half spreading rate and trend of this ridge are 2.73 cm/a and N152 degree respectively. A model is proposed to explain the evolution of the unstable RRF Rodriguez Triple Junction

Etude geophysique des dorsales de l'ocean Indien dans la region du point triple de Rodriguez

The Indian Ocean is dominated by as system of 3 mid-ocean ridges converging at the Rodriguez Triple Junction located near 25 degree 30'S and 70 degree E. Numerous studies carried out on these 3 ridges provided the basic information on spreading rates and spreading directions. In 1984 the R/V Jean Charcot conducted a detailed survey over the Rodriguez Triple Junction and over an axial ridge segment located on each of the 3 associated ridges. The ridge axes are cut by distinct rift valleys; the depth of these rift valleys is a function of spreading rates. The rift valleys are not in isostatic equilibrium, but show clear density and mass deficits (0.4 to 0.8 g.cm super(-3) for spreading rate of 1 cm/a and 0.1 to 0.3 g.cm super(-3) for spreading rates of 3 cm/a). The Rodriguez Triple Junction is unstable. The axis of the Central Indian Ridge is offset from the axis of the Southeast Indian Ridge at a velocity of 0.14 cm/a

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Structure and tectonic history of the southern Kerguelen Plateau (Indian Ocean) deduced from seismic reflection data

Early single-channel and recent multichannel seismic reflection data together reveal major tectonic events in the history of the Southern Kerguelen Plateau (SKP). The SKP was created by Early Cretaceous volcanism which was mainly subaerial. We estimate the age of the adjacent ocean basins to be similar to that of the plateau. Following termination of the main volcanism, the SKP began to subside and to accumulate sediment. A lower sedimentary megasequence was deposited at this time, primarily in depressions on the plateau. At about 88 Ma, tectonism affected the eastern Raggatt Basin; this tectonism may be related to faulting which created the steep eastern margin of the SKP. At about 72 Ma, predominant tectonic activity, characterized by widespread extension and uplift forming the tilted block morphology, occurred over large areas of the SKP. The extension centered along several NW-SE trending rift systems, in places creating well-preserved axial rifts. The largest structure of this kind, the Central SKP Uplift, lies along the center of the SKP; its relief increases from the southernmost part of the plateau toward the NW. The northernmost part of this uplift, the Banzare Bank, was elevated during rifting above sea level and was eroded. A second extensional structure, the SW Uplift, lies in the SW corner of the plateau, and other, smaller structures may also be present. The extension appears to have culminated in the initiation of the Southeast Indian Ridge at 43 Ma, but, at least in the Raggatt Basin, the two events were not continuous. Tectonic subsidence that was associated with the extension corresponds to deposition of a second megasequence, estimated to be about 1000 m thick on Banzare Bank. The subparallel trend of the rift systems on the SKP to the Southeast Indian Ridge and their timing suggest that the rearrangement of spreading in the South Indian Ocean at 43 Ma was not solely the result of the collision of India with Asia; it started earlier in association with other plate motions in the area

TENTATIVE D'INTERPRÉTATION DU SPECTRE DE LUMINESCENCE ET DES RAIES FAIBLES D'ABSORPTION DE CuCl AUX BASSES TEMPÉRATURES

Les énergies de liaison de quelques complexes excitoniques sont calculées en se basant sur des données numériques expérimentales nouvelles obtenues pour CuCl. Pour le complexe exciton donneur neutre, la théorie rigoureuse donnée récemment par Munschy est utilisée. Ces calculs permettent de suggérer une interprétation de quelques raies d'émission et d'absorption faibles de CuCl faisant appel, soit aux complexes excitoniques et impuretés étudiées, soit à un mécanisme d'émission simultanée d'un phonon et d'un photon. Bien que ces calculs n'expliquent pas encore toutes les raies observées, ils suggèrent une interprétation plausible d'un certain nombre d'entre elles et contribuent ainsi à une meilleure compréhension de ce spectre de CuCl.The binding energy of some exciton complexes is calculated on the basis of new experimental data for CuCl. For the binding energy of the exciton neutral donor complex, the recent rigorous theory of Munschy has been used. These calculations suggest the interpretation of some of the emission or weak absorption lines as related to exciton complexes or involving phonon cooperation. Though some of the lines remain unexplained these calculations suggest plausible interpretations for some of them and contributes to the understanding of the spectrum of CuCl