Trion dynamics in coupled double quantum wells. Electron density effects

We have studied the coherent dynamics of injected electrons when they are either free or bounded both in excitons and in trions (charged excitons). We have considered a remotely doped asymmetric double quantum well where an excess of free electrons and the direct created excitons generate trions. We have used the matrix density formalism to analyze the electron dynamics for different concentration of the three species. Calculations show a significant modification of the free electron inter-sublevel oscillations cWe have studied the coherent dynamics of injected electrons when they are aused by electrons bound in excitons and trions. Based on the present calculations we propose a method to detect trions through the emitted electromagnetic radiation or the current density.Comment: 14 pages, 13 figure

Optical Hall Effect in the Integer Quantum Hall Regime

Optical Hall conductivity $\sigma_{xy}(\omega)$ is measured from the Faraday rotation for a GaAs/AlGaAs heterojunction quantum Hall system in the terahertz frequency regime. The Faraday rotation angle ($\sim$ fine structure constant $\sim$ mrad) is found to significantly deviate from the Drude-like behavior to exhibit a plateau-like structure around the Landau-level filling $\nu=2$. The result, which fits with the behavior expected from the carrier localization effect in the ac regime, indicates that the plateau structure, although not quantized, still exists in the terahertz regime.Comment: 4 pages, 4 figure

Magnetic properties of PdAs2O6: a dilute spin system with an unusually high N\'eel temperature

The crystal structure and magnetic ordering pattern of PdAs2O6 were investigated by neutron powder diffraction. While the magnetic structure of PdAs2O6 is identical to the one of its isostructural 3d-homologue NiAs2O6, its N\'{e}el temperature (140 K) is much higher than the one of NiAs2O6 (30 K). This is surprising in view of the long distance and indirect exchange path between the magnetic Pd$^{2+}$ ions. Density functional calculations yield insight into the electronic structure and the geometry of the exchange-bond network of both PdAs2O6 and NiAs2O6, and provide a semi-quantitative explanation of the large amplitude difference between their primary exchange interaction parameters

Criticality on the international scene : quo vadis?

This paper brings a discussion on the current state-of-the-art in criticality assessment in an international context. It analyzes the status of resource criticality concepts and their calculation methods. The current practice often exhibits a common two-axis assessment framework but the way the two axes are further operationalized shows heterogeneous approaches. Apart from the two-axis as key element of criticality assessment, the scope of the materials, the role of substitution, the delineation of the supply chain and data, and indicator selection are addressed as key elements, The abovementioned criticality assessment practice is approached in function of the upcoming international debate on criticality. The paper tackles the role of criticality assessment in the context of the sustainability assessment toolbox and it proposes a clear distinction between criticality assessment and resilience to criticality. The insights offered in the paper may feed the international discussion in the identification of elements that may be harmonized and elements that may be better left open in function of the particular application

Distribution of Neuropeptide F-Like Immunoreactivity in the Eastern Subterranean Termite, Reticulitermes flavipes

The nervous system and gut of worker, soldier and alate castes of the eastern subterranean termite, Reticulitermes flavipes Kollar (Isoptera: Rhinotermitidae) were examined for immunoreactivity to an antiserum to Helicoverpa zea (Boddie) (Leipidoptera: Noctuidae) MP-I (QAARPRF-NH2), a truncated form of neuropeptide F. More than 145 immunostained axons and cell bodies were seen in the brain and all ganglia of the ventral nerve cord. Immunoreactive axons exiting the brain projected anteriorly to the frontal ganglion and posteriorly to the corpora cardiaca and corpora allata. In the stomatogastric nervous system, immunoreactive axons were observed over the surface of the foregut, salivary glands, midgut and rectum. These axons originated in the brain and from 15–25 neurosecretory cells on the foregut. Staining patterns were consistent between castes, with the exception of immunostaining observed in the optic lobes of alates. At least 600 immunoreactive endocrine cells were evenly distributed in the midguts of all castes with higher numbers present in the worker caste. Immunostaining of cells in the nervous system and midgut was blocked by preabsorption of the antiserum with Hez MP-I but not by a peptide having only the RF-NH2 in common. This distribution suggests NPF-like peptides coordinate feeding and digestion in all castes of this termite species

Detection and correction of the misplacement error in THz Spectroscopy by application of singly subtractive Kramers-Kronig relations

In THz reflection spectroscopy the complex permittivity of an opaque medium is determined on the basis of the amplitude and of the phase of the reflected wave. There is usually a problem of phase error due to misplacement of the reference sample. Such experimental error brings inconsistency between phase and amplitude invoked by the causality principle. We propose a rigorous method to solve this relevant experimental problem by using an optimization method based upon singly subtractive Kramers-Kronig relations. The applicability of the method is demonstrated for measured data on an n-type undoped (100) InAs wafer in the spectral range from 0.5 up to 2.5 THz.Comment: 16 pages, 5 figure