Electronic structure of ferromagnetic semiconductor Ga1-xMnxAs probed by sub-gap magneto-optical spectroscopy

We employ Faraday and Kerr effect spectroscopy in the infrared range to investigate the electronic structure of Ga1-xMnxAs near the Fermi energy. The band structure of this archetypical dilute-moment ferromagnetic semiconductor has been a matter of controversy, fueled partly by previous measurements of the unpolarized infrared absorption and their phenomenological impurity-band interpretation. The infrared magneto-optical effects we study arise directly from the spin-splitting of the carrier bands and their chiral asymmetry due to spin-orbit coupling. Unlike the unpolarized absorption, they are intimately related to ferromagnetism and their interpretation is much more microscopically constrained in terms of the orbital character of the relevant band states. We show that the conventional theory of the disordered valence band with dominant As p-orbital character and coupled by kinetic-exchange to Mn local moments accounts semi-quantitatively for the overall characteristics of the measured infrared magneto-optical spectra.Comment: 4 pages 3 figure

Origin of Magnetic Circular Dichroism in GaMnAs: Giant Zeeman Splitting versus Spin Dependent Density of States

We present a unified interpretation of experimentally observed magnetic circular dichroism (MCD) in the ferromagnetic semiconductor (Ga,Mn)As, based on theoretical arguments, which demonstrates that MCD in this material arises primarily from a difference in the density of spin-up and spin-down states in the valence band brought about by the presence of the Mn impurity band, rather than being primarily due to the Zeeman splitting of electronic states.Comment: 4+ pages, 4 figure

Hematite-rich concretions from Mesoproterozoic Vindhyan sandstone in northern India: a terrestrial Martian 'blueberries' analogue with a difference

We report here hematite-rich concretions observed in the sandstone of the Mesoproterozoic Vindhyan Supergroup of rocks occurring in parts of Bihariya, Uttar Pradesh, northern India. These concretions are similar to `blueberries' from Mars and their terrestrial analogues reported from the Jurassic Navajo Sandstone in Utah, USA. The presence of diagenetically formed hematite concretions gave the first confirmation of the presence of liquid water in the red planet in the past. We report here the detailed morphology, petrography, mineral chemistry, magnetic susceptibility characteristics and spectral radiometric data of hematite-rich concretions observed in the Vindhyan sandstone. These are compared with `blueberries' from Mars and other similar terrestrial analogues reported from different parts of the world. In spite of similarities, these hematite-rich concretions are strikingly distinct in having a nucleus and alternate iron-rich and iron-poor rims unlike other global occurrences. In addition, we document here outcrop scale evidence of possible fluid pathways considered responsible for the development of the concretions

(Blue) Growth accounting in small-scale European Union fleets

Fisheries account for one-third of the total jobs in the global ocean economies. Small scale fleets (SSF) fisheries are the main segment from the number of jobs point of view, and in the EU, SSF account for over 40% of employment in the fisheries sector. Given this marine employment source, it is important to analyse SSF's productivity growth. This was done using Total Factor Productivity (TFP), which is dened as the portion of output not explained by the traditionally measured inputs of labour, energy and capital used in production. TFP calculation is relevant to understand the technology evolution in fisheries and as a reference for management assessment. TFP was calculated for SSF in two EU main sea areas, the Mediterranean (FAO area 37) and the North-East Atlantic (FAO area 27). Constant elasticity production functions were used to analyse the intensity of the use of production factors and how these are substituted or complemented when producing. Additionally, TFP was corrected by stock evolution indexes to evaluate the EU conservation policy. Results showed how the TFP presented signs of stagnation when stocks status were considered. This implies a low technological evolution and that the use of production factors is to be reduced in the following years. It was concluded that in the North-East Atlantic the EU conservation policy is obtaining the objective of restoring fish stocks and contributing to maintaining the productivity. In the Mediterranean, the stocks are not being restored, therefore not contributing to growth as a production factor. Finally, it is concluded that in neither areas the conservation policy is enough to provide positive productivity trends.JRC.D.2-Water and Marine Resource