Perfil profissional no meio rural: subsídios para diagnóstico e definição de estratégias: cadeias produtivas da apicultura, bovinocultura leiteira e ovinocultura.

bitstream/CNPDIA-2009-09/12002/1/DOC40_2008.pd

Quantum criticality of semi-Dirac fermions in 2 + 1 dimensions

Two-dimensional semi-Dirac fermions are quasiparticles that disperse linearly in one direction and quadratically in the other. We investigate instabilities of semi-Dirac fermions toward charge and spin density wave and superconducting orders, driven by short-range interactions. We analyze the critical behavior of the Yukawa theories for the different order parameters using Wilson momentum shell renormalization group. We generalize to a large number Nf of fermion flavors to achieve analytic control in 2+1 dimensions and calculate critical exponents at one-loop order, systematically including 1/Nf corrections. The latter depend on the specific form of the bosonic infrared propagator in 2+1 dimensions, which needs to be included to regularize divergencies. The 1/Nf corrections are surprisingly small, suggesting that the expansion is well controlled in the physical dimension. The order parameter correlations inherit the electronic anisotropy of the semi-Dirac fermions, leading to correlation lengths that diverge along the spatial directions with distinct exponents, even at the mean-field level. We conjecture that the proximity to the critical point may stabilize novel modulated order phases

Competition between excitonic gap generation and disorder scattering in graphene

We study the disorder effect on the excitonic gap generation caused by strong Coulomb interaction in graphene. By solving the self-consistently coupled equations of dynamical fermion gap $m$ and disorder scattering rate $\Gamma$, we found a critical line on the plane of interaction strength $\lambda$ and disorder strength $g$. The phase diagram is divided into two regions: in the region with large $\lambda$ and small $g$, $m \neq 0$ and $\Gamma = 0$; in the other region, $m = 0$ and $\Gamma \neq 0$ for nonzero $g$. In particular, there is no coexistence of finite fermion gap and finite scattering rate. These results imply a strong competition between excitonic gap generation and disorder scattering. This conclusion does not change when an additional contact four-fermion interaction is included. For sufficiently large $\lambda$, the growing disorder may drive a quantum phase transition from an excitonic insulator to a metal.Comment: 8 pages, 1 figur

Surface superconductivity in multilayered rhombohedral graphene: Supercurrent

The supercurrent for the surface superconductivity of a flat-band multilayered rhombohedral graphene is calculated. Despite the absence of dispersion of the excitation spectrum, the supercurrent is finite. The critical current is proportional to the zero-temperature superconducting gap, i.e., to the superconducting critical temperature and to the size of the flat band in the momentum space

Hidden charge order of interacting Dirac fermions on the honeycomb lattice

We consider the extended half-filled Hubbard model on the honeycomb lattice for second nearest-neighbor interactions. Using a functional integral approach, we find that collective fluctuations suppress topological states and instead favor charge ordering, in agreement with previous numerical studies. However, we show that the critical point is not of the putative semimetal-Mott insulator variety. Due to the frustrated nature of the interactions, the ground state is described by a novel hidden metallic charge order with semi-Dirac excitations. We conjecture that this transition is not in the Gross-Neveu universality class

Plataforma de logística.

bitstream/item/89739/1/Proci-07.00198.pd

Diagnóstico do sistema produtivo do cajueiro no Sudeste do Piauí.

Este trabalhou objetivou coletar informações preliminares sobre os sistemas de produção empregados na Microrregião Sudeste piauiense, com ênfase nos fatores fitossanitários mais limitantes e nos aspectos socieconômicos relevantes para o desenvolvimento da cultura do cajueiro.bitstream/CNPAT-2010/9018/1/Ct-083.pd

Magnetic structure and critical behavior of GdRhIn5_{5}: resonant x-ray diffraction and renormalization group analysis

The magnetic structure and fluctuations of tetragonal GdRhIn5 were studied by resonant x-ray diffraction at the Gd LII and LIII edges, followed by a renormalization group analysis for this and other related Gd-based compounds, namely Gd2IrIn8 and GdIn3. These compounds are spin-only analogs of the isostructural Ce-based heavy-fermion superconductors. The ground state of GdRhIn5 shows a commensurate antiferromagnetic spin structure with propagation vector tau = (0,1/2, 1/2), corresponding to a parallel spin alignment along the a-direction and antiparallel alignment along b and c. A comparison between this magnetic structure and those of other members of the Rm(Co,Rh,Ir)n In3m+2n family (R =rare earth, n = 0, 1; m = 1, 2) indicates that, in general, tau is determined by a competition between first-(J1) and second-neighbor(J2) antiferromagnetic (AFM) interactions. While a large J1 /J2 ratio favors an antiparallel alignment along the three directions (the so-called G-AFM structure), a smaller ratio favors the magnetic structure of GdRhIn5 (C-AFM). In particular, it is inferred that the heavy-fermion superconductor CeRhIn5 is in a frontier between these two ground states, which may explain its non-collinear spiral magnetic structure. The critical behavior of GdRhIn5 close to the paramagnetic transition at TN = 39 K was also studied in detail. A typical second-order transition with the ordered magnetization critical parameter beta = 0.35 was experimentally found, and theoretically investigated by means of a renormalization group analysis.Comment: 22 pages, 4 figure