820 research outputs found

    Optical Conductivity of Ferromagnetic Semiconductors

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    The dynamical mean field method is used to calculate the frequency and temperature dependent conductivity of dilute magnetic semiconductors. Characteristic qualitative features are found distinguishing weak, intermediate, and strong carrier-spin coupling and allowing quantitative determination of important parameters defining the underlying ferromagnetic mechanism

    Consistency of local perceptions of climate change in the Kangchenjunga Himalaya landscape

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    The Himalaya is experiencing rapid climate change that is likely to significantly impact local ecosystems, biodiversity, agriculture and human well-being. However, the scientific community has been slow to examine the extent and consequences of climate change. Local communities have been coping with environmental change since millennia. Thus they often have considerable knowledge about environmental change and means to cope with its consequences. We (a) examined the perceptions of local communities about climate change and its impacts on ecosystems, biodiversity, agriculture and livelihoods in the Kangchenjunga Himalayas region; (b) analysed the consistency of perceptions across geographical regions, and (c) assessed the conformity between local perceptions and scientific evidence. Our study is based on surveys conducted in 576 households, focus group discussions, key informant surveys and direct observations. The results show that people in the Kangchenjunga Himalayas region have considerable knowledge of climate change and its effects on the weather, ecosystems, biodiversity and agriculture. These perceptions are consistent across the region and conform to scientific findings

    Transition temperature of ferromagnetic semiconductors: a dynamical mean field study

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    We formulate a theory of doped magnetic semiconductors such as Ga1−x_{1-x}Mnx_xAs which have attracted recent attention for their possible use in spintronic applications. We solve the theory in the dynamical mean field approximation to find the magnetic transition temperature TcT_c as a function of magnetic coupling strength JJ and carrier density nn. We find that TcT_c is determined by a subtle interplay between carrier density and magnetic coupling.Comment: 4 pages, 4 figure

    Photoemission studies of Ga1−x_{1-x}Mnx_{x}As: Mn-concentration dependent properties

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    Using angle-resolved photoemission, we have investigated the development of the electronic structure and the Fermi level pinnning in Ga1−x_{1-x}Mnx_{x}As with Mn concentrations in the range 1--6%. We find that the Mn-induced changes in the valence-band spectra depend strongly on the Mn concentration, suggesting that the interaction between the Mn ions is more complex than assumed in earlier studies. The relative position of the Fermi level is also found to be concentration-dependent. In particular we find that for concentrations around 3.5--5% it is located very close to the valence-band maximum, which is in the range where metallic conductivity has been reported in earlier studies. For concentration outside this range, larger as well as smaller, the Fermi level is found to be pinned at about 0.15 eV higher energy.Comment: REVTeX style; 7 pages, 3 figure

    Carrier induced ferromagnetism in diluted magnetic semi-conductors

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    We present a theory for carrier induced ferromagnetism in diluted magnetic semi-conductor (DMS). Our approach treats on equal footing quantum fluctuations within the RPA approximation and disorder within CPA. This method allows for the calculation of TcT_c, magnetization and magnon spectrum as a function of hole, impurity concentration and temperature. It is shown that, sufficiently close to TcT_c, and within our decoupling scheme (Tyablicov type) the CPA for the itinerant electron gas reduces to the Virtual Crystal Approximation. This allows, in the low impurity concentration and low density of carriers to provide analytical expression for TcT_c. For illustration, we consider the case of Ga1−cMncAsGa_{1-c}Mn_{c}As and compare our results with available experimental data.Comment: 5 figures included. to appear in Phys. Rev. B (brief report
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