23,283 research outputs found
Chiral spin-orbital liquids with nodal lines
Strongly correlated materials with strong spin-orbit coupling hold promise
for realizing topological phases with fractionalized excitations. Here we
propose a chiral spin-orbital liquid as a stable phase of a realistic model for
heavy-element double perovskites. This spin liquid state has Majorana fermion
excitations with a gapless spectrum characterized by nodal lines along the
edges of the Brillouin zone. We show that the nodal lines are topological
defects of a non-Abelian Berry connection and that the system exhibits
dispersing surface states. We discuss some experimental signatures of this
state and compare them with properties of the spin liquid candidate Ba_2YMoO_6.Comment: 5 pages + supplementary materia
Non-Collinear Ferromagnetic Luttinger Liquids
The presence of electron-electron interactions in one dimension profoundly
changes the properties of a system. The separation of charge and spin degrees
of freedom is just one example. We consider what happens when a system
consisting of a ferromagnetic region of non-collinearity, i.e. a domain wall,
is coupled to interacting electrons in one-dimension (more specifically a
Luttinger liquid). The ferromagnetism breaks spin charge separation and the
presence of the domain wall introduces a spin dependent scatterer into the
problem. The absence of spin charge separation and the effects of the electron
correlations results in very different behaviour for the excitations in the
system and for spin-transfer-torque effects in this model.Comment: 6 pages, submitted to Journal of Physics: Conference Series for JEMS
201
Dirac and Klein-Gordon particles in one-dimensional periodic potentials
We evaluate the dispersion relation for massless fermions, described by the
Dirac equation, and for zero-spin bosons, described by the Klein-Gordon
equation, moving in two dimensions and in the presence of a one-dimensional
periodic potential. For massless fermions the dispersion relation shows a zero
gap for carriers with zero momentum in the direction parallel to the barriers
in agreement with the well-known "Klein paradox". Numerical results for the
energy spectrum and the density of states are presented. Those for fermions are
appropriate to graphene in which carriers behave relativistically with the
"light speed" replaced by the Fermi velocity. In addition, we evaluate the
transmission through a finite number of barriers for fermions and zero-spin
bosons and relate it with that through a superlattice.Comment: 9 pages, 12 figure
Efeito de área e densidade de árvores sobre a probabilidade de ocupação de manchas florestais no Pantanal por corujas pretas (Strix huhula).
A fragmentação e a degradação de habitats estão entre os principais problemas para a conservação da biodiversidade. No Pantanal, muitas vezes considera do o ecossistema mais preservado do Brasil, a criação de gado bovino há mais de dois séculos na região se baseia em práticas de manejo da vegetação utilizadas de formas diversas, em especial o uso do fogo. Entretanto, os efeitos de distúrbios crônicos sobre a estrutura de habitats e seus efeitos sobre as espécies não tem sido estudados. Nós utilizamos a modelagem de ocupação para avaliar os efeitos da estrutura de habitats forestais sobre a coruja preta, com base em amostragem em 36 pontos localizados na porção oeste da Nhecolândia, Pantanal, Corumbá, MS, entre fevereiro e junho de 2013. O melhor modelo de probabilidade de ocupação inclui tanto a área das manchas florestais qunanto a densidade de árevores maiorres que 50 cm de circunferencia á altura do peito. Os resultados indicam que distúrbios crônicos podem estar afetando a estrutura de habitats, por interferencia na dinamica da vegetação, e consequentemente afetando espécies da fauna associadas à habitats florestais, como a coruja preta
Adubação N-P-K para o abacaxizeiro BRS Imperial para o Extremo Sul da Bahia.
A Embrapa Mandioca e Fruticultura lançou em 2003 o híbrido de abacaxizeiro BRS Imperial, que tem grande potencial de se estabelecer amplamente nas regiões produtoras, pela sua resistência à fusariose, principal doença da cultura, por possuir folhas sem espinhos e por seus frutos apresentarem excelentes características físico-químicas e boa aparência.bitstream/item/119347/1/comunicado-tecnico-158-Atual.pd
Métodos de aplicação de bactérias diazotróficas em cana-soca para fins de determinação da eficiência agronômica.
bitstream/item/42766/1/COT117-09.pd
Density functional investigations of defect induced mid-gap states in graphane
We have carried out ab initio electronic structure calculations on graphane
(hydrogenated graphene) with single and double vacancy defects. Our analysis of
the density of states reveal that such vacancies induce the mid gap states and
modify the band gap. The induced states are due to the unpaired electrons on
carbon atoms. Interestingly the placement and the number of such states is
found to be sensitive to the distance between the vacancies. Furthermore we
also found that in most of the cases the vacancies induce a local magnetic
moment.Comment: 15 page
Block Copolymer at Nano-Patterned Surfaces
We present numerical calculations of lamellar phases of block copolymers at
patterned surfaces. We model symmetric di-block copolymer films forming
lamellar phases and the effect of geometrical and chemical surface patterning
on the alignment and orientation of lamellar phases. The calculations are done
within self-consistent field theory (SCFT), where the semi-implicit relaxation
scheme is used to solve the diffusion equation. Two specific set-ups, motivated
by recent experiments, are investigated. In the first, the film is placed on
top of a surface imprinted with long chemical stripes. The stripes interact
more favorably with one of the two blocks and induce a perpendicular
orientation in a large range of system parameters. However, the system is found
to be sensitive to its initial conditions, and sometimes gets trapped into a
metastable mixed state composed of domains in parallel and perpendicular
orientations. In a second set-up, we study the film structure and orientation
when it is pressed against a hard grooved mold. The mold surface prefers one of
the two components and this set-up is found to be superior for inducing a
perfect perpendicular lamellar orientation for a wide range of system
parameters
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