Introductory Chapter: Mineral Exploration from the Point of View of Geophysicists

International audienc

Aharonov-Bohm Oscillations in Photoluminescence from Charged Exciton in Quantum Tubes

The oscillation of photoluminescence peak energies is observed in InAs quantum tubes depending on the magnetic flux through the tube. The oscillation is shown to be due to the Aharonov-Bohm effect of a charged exciton in a quantum tube. No quadratic shift in photoluminescence peak energies is observed, which is a characteristic feature of a thin quantum tube with a single channel surrounding the magnetic flux through the tube.Comment: 14 pages, 4 figure

Transport barrier onset and edge turbulence shortfall in fusion plasmas

Turbulent plasmas notably self-organize to higher energy states upon application of additional free energy sources or modification of edge operating conditions. Mechanisms whereby such bifurcations occur have been actively debated for decades. Enhanced confinement occurs at the plasma edge, where a shortfall of predicted turbulence intensity has been puzzling scientists for decades. We show, from the primitive kinetic equations that both problems are connected and that interplay of confined plasma turbulence with its material boundaries is essential to curing the shortfall of predicted turbulence and to triggering spontaneous transport barrier onset at the plasma edge. Both problems determine access to improved confinement and are central to fusion research. A comprehensive discussion of the underlying mechanisms is proposed. These results, highly relevant to the quest for magnetic fusion may also be generic to many problems in fluids and plasmas where turbulence self-advection is active

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.

Effect of fermionic components on trion-electron scattering

To test the validity of replacing a composite fermion by an elementary fermion, we here calculate the transition rate from a state made of one free electron and one trion to a similar electron-trion pair, through the time evolution of such a pair induced by Coulomb interaction between elementary fermions. To do it in a convenient way, we describe the trion as one electron interacting with one exciton, and we use the tools we have developed in the new composite-exciton many-body theory. The trion-electron scattering contains a direct channel in which ``in'' and ``out'' trions are made with the same fermions, and an exchange channel in which the ``in'' free electron becomes one of the ``out'' trion components. As expected, momenta are conserved in these two channels. The direct scattering is found to read as the bare Coulomb potential between elementary particles multiplied by a form factor which depends on the ``in'' and ``out'' trion relative motion indices $\eta$ and $\eta'$, this factor reducing to $\delta_{\eta\eta'}$ in the zero momentum transfer limit: In this direct channel, the trion at large distance reacts as an elementary particle, its composite nature showing up for large momentum transfer. On the contrary, the fact that the trion is not elementary does affect the exchange channel for all momentum transfers. We thus conclude that a 3-component fermion behaves as an elementary fermion for direct processes in the small momentum transfer limit only

Preliminary report of the First season of the Saudi-French mission in al-Yamāma. Al-Kharj area (20 September-21 October 2011)

Report of the archaeological, geophysical, archaeozoological and topographical activities of the French-Saudi mission in the oasis of al-Kharj, 80 km South of Riyadh, in the Central Province of Saudi Arabia carried out from September 20th to October 21st 2011. It includes chapters on: - The geographic and historical setting - The present issues for a study of al-Kharj area - An historiography of the exploration of al-Kharj area - Description on the Registration system - Details of the Historical survey of the oasis - Report of the exploration of the site of al-Yamāma (geophysical survey, topographical survey, archaeological sounding, zooarchaeological study) - Ceramic study An abstract in Arabic is available at the end of the report

Do ridge-ridge-fault triple junctions exist on Earth? Evidence from the Aden-Owen-Carlsberg junction in the NW Indian Ocean

International audienceThe triple junctions predicted to be ridge^ridge^fault (RRF) types on the basis of large- scale plate motions are theAzores triple junction between theGloria Fault and theMid-AtlanticRidge, the Juan Fernandez triple junction between the ChileTransform and the East Paci¢c Rise and the Aden^ Owen^Carlsberg (AOC) triple junction between theOwen fracture zone (OFZ) and theCarlsberg and Sheba ridges. In the ¢rst two cases, the expected RRF triple junction does not exist because the transform fault arm of the triple junction has evolved into a divergent boundary before connecting to the ridges.Here, we report the results of a marine geophysical survey of the AOC triple junction, which took place in 2006 aboard the R/VBeautemps-Beaupre¤.We show that a rift basin currently forms at the southern end of theOFZ, indicating that a divergent plate boundary between Arabia and India is developing at the triple junction.The connection of this boundary with the Carlsberg and Sheba ridges is not clearly delineated and the triple junction presently corresponds to awidespread zone of distributed deformation.The AOC triple junction appears to be in a transient stage between a former triple junction of the ridge^fault^fault type and a future triple junction of the ridge^ridge^ridge (RRR) type. Consequently, the known three examples of potential RRF triple junctions are actually of the RRR type, and RRF triple junctions do not presently exist on Eart