Theory of Andreev reflection in a two-orbital model of iron-pnictide superconductors

A recently developed theory for the problem of Andreev reflection between a normal metal (N) and a multiband superconductor (MBS) assumes that the incident wave from the normal metal is coherently transmitted through several bands inside the superconductor. Such splitting of the probability amplitude into several channels is the analogue of a quantum waveguide. Thus, the appropriate matching conditions for the wave function at the N/MBS interface are derived from an extension of quantum waveguide theory. Interference effects between the transmitted waves inside the superconductor manifest themselves in the conductance. We provide results for a FeAs superconductor, in the framework of a recently proposed effective two-band model and two recently proposed gap symmetries: in the sign-reversed s-wave ($\Delta\cos(k_x)\cos(k_y)$) scenario resonant transmission through surface Andreev bound states (ABS) at nonzero energy is found as well as destructive interference effects that produce zeros in the conductance; in the extended s-wave ($\Delta[\cos(k_x)+\cos(k_y)]$) scenario no ABS at finite energy are found.Comment: 4 pages, 5 figure

Temperature oscillations of magnetization observed in nanofluid ferromagnetic graphite

We report on unusual magnetic properties observed in the nanofluid room-temperature ferromagnetic graphite (with an average particle size of l=10nm). More precisely, the measured magnetization exhibits a low-temperature anomaly (attributed to manifestation of finite size effects below the quantum temperature) as well as pronounced temperature oscillations above T=50K (attributed to manifestation of the hard-sphere type pair correlations between ferromagnetic particles in the nanofluid)

Anomalous Hall effect in superconductors with spin-orbit interaction

We calculate the anomalous Hall conductance of superconductors with spin-orbit interaction and with either uniform or local magnetization. In the first case we consider a uniform ferromagnetic ordering in a spin triplet superconductor, while in the second case we consider a conventional s-wave spin singlet superconductor with a magnetic impurity (or a diluted set of magnetic impurities). In the latter case we show that the anomalous Hall conductance can be used to track the quantum phase transition, that occurs when the spin coupling between the impurity and electronic spin density exceeds a certain critical value. In both cases we find that for large spin-orbit coupling the superconductivity is destroyed and the Hall conductance oscillates strongly.Comment: 10 pages, 6 figure

Random Sequential Adsorption: From Continuum to Lattice and Pre-Patterned Substrates

The random sequential adsorption (RSA) model has served as a paradigm for diverse phenomena in physical chemistry, as well as in other areas such as biology, ecology, and sociology. In the present work, we survey aspects of the RSA model with emphasis on the approach to and properties of jammed states obtained for large times in continuum deposition versus that on lattice substrates, and on pre-patterned surfaces. The latter model has been of recent interest in the context of efforts to use pre-patterning as a tool to improve selfassembly in micro- and nanoscale surface structure engineering

Local Moment Formation in the Periodic Anderson Model with Superconducting Correlations

We study local moment formation in the presence of superconducting correlations among the f-electrons in the periodic Anderson model. Local moments form if the Coulomb interaction U>U_cr. We find that U_cr is considerably stronger in the presence of superconducting correlations than in the non-superconducting system. Our study is done for various values of the f-level energy and electronic density. The smallest critical U_cr values occur for the case where the number of f- electrons per site is equal to one. In the presence of d-wave superconducting correlations we find that local moment formation presents a quantum phase transition as function of pressure. This quantum phase transition separates a region where local moments and d-wave superconductivity coexist from another region characterized by a superconducting ground state with no local moments. We discuss the possible relevance of these results to experimental studies of the competition between magnetic order and superconductivity in CeCu_2Si_2.Comment: 4 pages. accepted for publication in Phys. Rev.

Germinação de Cratylia argentea em diferentes graus de maturação.

Edição dos Anais do XVII Congresso Brasileiro de Sementes, Natal, 2011

Caracterização da matéria orgânica e mineralógica dos solos das bacias dos rios Acre e Iaco, estado do Acre.

Na região Amazônica, o uso da terra tem levado, no decorrer dos anos, a um mosaico de agroecossistemas que caracterizam e registram a resposta do ambiente às suas alterações. Os conhecimentos pedoambientais e a ação antrópica nestes ambientes são de importância fundamental para o melhor uso dos ecossistemas. O objetivo do presente trabalho foi estudar duas bacias contíguas com componentes pedológicos distintos utilizando como base de estratificação a matéria orgânica e a mineralogia de forma a subsidiar o manejo dos solos nesta região. Nos perfis descritos e coletados nas duas bacias de estudo, bacia do rio Acre e Iaco, foram realizados: extração e fracionamento de substâncias húmicas, fracionamento físico da matéria orgânica para obtenção da fração leve e análises de difratometria por raios X, para análises mineralógicas. Os resultados revelaram o domínio de frações húmicas em superfície, sempre reduzindo em profundidade e diferenças mineralógicas nas bacias estudadas, onde a bacia do rio Acre apresentou minerais mais evoluídos como caulinita e gibbsita e na bacia do rio Iaco, mineralogia do tipo 2:1 como vermiculita e esmectita, que revela o caráter jovens de seus solos e uma maior vulnerabilidade a ação antrópica

Resposta de cultivares de cebola (Allium cepa L.) a doses de fósforo em cultivo orgânico no Vale do São Francisco.

Suplemento. Edição dos Trabalhos do 49 Congresso Brasileiro de Olericultura, Águas de Lindóia, ago. 2009

Degradabilidade ruminal da palma forrageira e do atriplex em bovinos.

Este trabalho avaliou a influência de dietas contendo substituições parciais da palma forrageira pela atriplex sobre a degradabilidade ruminal da matéria seca e fibra em detergente neutro do feno de atriplex e da palma forrageira em bovinos