Coexistence of Pairing Tendencies and Ferromagnetism in a Doped Two-Orbital Hubbard Model on Two-Leg Ladders

Using the Density Matrix Renormalization Group and two-leg ladders, we investigate an electronic two-orbital Hubbard model including plaquette diagonal hopping amplitudes. Our goal is to search for regimes where charges added to the undoped state form pairs, presumably a precursor of a superconducting state.For the electronic density $\rho=2$, i.e. the undoped limit, our investigations show a robust $(\pi,0)$ antiferromagnetic ground state, as in previous investigations. Doping away from $\rho=2$ and for large values of the Hund coupling $J$, a ferromagnetic region is found to be stable. Moreover, when the interorbital on-site Hubbard repulsion is smaller than the Hund coupling, i.e. for $U'<J$ in the standard notation of multiorbital Hubbard models, our results indicate the coexistence of pairing tendencies and ferromagnetism close to $\rho=2$. These results are compatible with previous investigations using one dimensional systems. Although further research is needed to clarify if the range of couplings used here is of relevance for real materials, such as superconducting heavy fermions or pnictides, our theoretical results address a possible mechanism for pairing that may be active in the presence of short-range ferromagnetic fluctuations.Comment: 8 pages, 4 Fig

Topological confinement in graphene bilayer quantum rings

We demonstrate the existence of localized electron and hole states in a ring-shaped potential kink in biased bilayer graphene. Within the continuum description, we show that for sharp potential steps the Dirac equation describing carrier states close to the K (or K') point of the first Brillouin zone can be solved analytically for a circular kink/anti-kink dot. The solutions exhibit interfacial states which exhibit Aharonov-Bohm oscillations as functions of the height of the potential step and/or the radius of the ring

Variabilidade genética entre acessos de amendoim.

O objetivo deste trabalho foi avaliar a variabilidade genética entre 29 acessos de amendoim (Arachis hypogaea L.), por meio de marcadores moleculares randômicos (DNA polimórfico amplificado ao acaso - RAPD). O ensaio molecular foi realizado com 31 iniciadores, dos quais 12 (39%) mostraram polimorfismo. Observou-se o total de 145 fragmentos amplificados, dos quais 35 (24%) foram polimórficos, com média de 4,67 fragmentos por iniciador e 1,13 fragmento polimórfico por iniciador. Pelo dendrograma, observou-se que os acessos foram separados em dois grupos com 89% de similaridade. Esta distribuição mostra a variabilidade existente entre os acessos das diferentes variedades botânicas, uma vez que acessos da subespécie fastigiata estão presentes nos dois grupos principais, e os acessos da subespécie hypogaea estão distribuídos pelos subgrupos A e B do grupo II do dendograma. The objective of this study was to evaluate the genetic variability among 29 accessions of peanut (Arachis hypogaea L.) by means of random molecular markers (random amplified polimorphic DNA - RAPD). The molecular assay was performed with 31 primers, of which 12 (39%) revealed polymorphism. It was observed a total of 145 amplified fragments, of which 35 (24%) were polymorphic, with an average of 4.67 fragments by primer and 1.13 polymorphic fragment by primer. It was observed through the dendrogram that the accessions were separated into two groups with 89% of similarity. This distribution shows the variability among the accessions of the different botanical varieties, since the accessions of subspecie fastigiata are present in two principal groups, and the accessions of subspecie hypogaea are distributed in subgroups A and B from dendrogram group II

An analysis of the elastic properties of a porous aluminium oxide film by means of indentation techniques

The elastic modulus of thin films can be directly determined by instrumented indentation when the indenter penetration does not exceed a fraction of the film thickness, depending on the mechanical properties of both film and substrate. When it is not possible, application of models for separating the contribution of the substrate is necessary. In this work, the robustness of several models is analyzed in the case of the elastic modulus determination of a porous aluminium oxide film produced by anodization of an aluminium alloy. Instrumented indentation tests employing a Berkovich indenter were performe data nanometric scale, which allowed a direct determination of the film elastic modulus, whose value was found to be approximately 11 GPa. However, at a micrometric scale the elastic modulus tends toward the value corresponding to the substrate, of approximately 73 GPa. The objective of the present work is to apply different models for testing their consistency over the complete set of indentation data obtained from both classical tests in microindentation and the continuous stiffness measurement mode in nanoindentation. This approach shows the continuity between the two scales of measurement thus allowing a better representation of the elastic modulus variation between two limits corresponding to the substrate and film elastic moduli. Gao's function proved to be the best to represen the elastic modulus variation

Avaliação do potencial de estirpes de rizóbio em fixar nitrogênio associadas ao feijão-caupi em Petrolina-PE.

O feijão-caupi é uma cultura leguminosa de grande importância para a alimentação humana, constituindo-se em uma fonte de proteína para a maioria da população rural. A eficiência de diferentes estirpes de rizóbio em fixar o nitrogênio atmosférico em associação com o feijão-caupi foi testada ao nível de campo na Estação Experimental da Caatinga, da Embrapa Semi-Árido, localizada no município de Petrolina-PE (09o23'S e 40o30'W, altitude: 350 m). O experimento foi implantado em condições de sequeiro, com delineamento de blocos ao acaso e seis repetições, constando de seis tratamentos, sendo quatro estirpes de rizóbio - BR 3267, BR 3299, BR 33o1 e BR 3302, uma dose de nitrogênio mineral - 50 kg ha-1 e uma testemunha. Aos trinta dias após o plantio, o número e peso seco de nódulos, peso de matéria seca e concentração de nitrogênio na parte aérea da planta foram determinados. Todas as estirpes superaram significativamente o tratamento testemunha, tanto em número como em peso seco de nódulos, denotando uma alta eficiência em nodular as raízes de feijão-caupi em relação às estirpes de rizóbio existentes no solo da área experimental