The Electronic States of Two Oppositely doped Mott Insulators Bilayers

We study the effect of Coulomb interaction between two oppositely doped low-dimensional tJ model systems. We exactly show that, in the one-dimensional case, an arbitrarily weak interaction leads to the formation of charge neutral electron-hole pairs. We then use two different mean-field theories to address the two-dimensional case, where inter-layer excitons also form and condense. We propose that this results in new features which have no analog in single layers, such as the emergence of an insulating spin liquid phase. Our simple bilayer model might have relevance to the physics of doped Mott insulator interfaces and of the new four layer Ba2CaCu4O8 compound.Comment: 4 pages, 1 figur

Doped carrier formulation and mean-field theory of the tt't''J model

In the generalized-tJ model the effect of the large local Coulomb repulsion is accounted for by restricting the Hilbert space to states with at most one electron per site. In this case the electronic system can be viewed in terms of holes hopping in a lattice of correlated spins, where holes are the carriers doped into the half-filled Mott insulator. To explicitly capture the interplay between the hole dynamics and local spin correlations we derive a new formulation of the generalized-tJ model where doped carrier operators are used instead of the original electron operators. This ``doped carrier'' formulation provides a new starting point to address doped spin systems and we use it to develop a new, fully fermionic, mean-field description of doped Mott insulators This mean-field approach reveals a new mechanism for superconductivity, namely spinon-dopon mixing, and we apply it to the tt't''J model as of interest to high-temperature superconductors. In particular, we use model parameters borrowed from band calculations and from fitting ARPES data to obtain a mean-field phase diagram that reproduces semi-quantitatively that of hole and electron doped cuprates. The mean-field approach hereby presented accounts for the local antiferromagnetic and d-wave superconducting correlations which, we show, provide a rational for the role of t' and t'' in strengthening superconductivity as expected by experiments and other theoretical approaches. As we discuss how t, t' and t'' affect the phase diagram, we also comment on possible scenarios to understand the differences between as-grown and oxygen reduced electron doped samples.Comment: 17 pages, 2 figures. Homepage http://dao.mit.edu/~wen

Analysis of the temperature influence on Langmuir probe measurements on the basis of gyrofluid simulations

The influence of the temperature and its fluctuations on the ion saturation current and the floating potential, which are typical quantities measured by Langmuir probes in the turbulent edge region of fusion plasmas, is analysed by global nonlinear gyrofluid simulations for two exemplary parameter regimes. The numerical simulation facilitates a direct access to densities, temperatures and the plasma potential at different radial positions around the separatrix. This allows a comparison between raw data and the calculated ion saturation current and floating potential within the simulation. Calculations of the fluctuation-induced radial particle flux and its statistical properties reveal significant differences to the actual values at all radial positions of the simulation domain, if the floating potential and the temperature averaged density inferred from the ion saturation current is used.Comment: Submitted to Plasma Physics and Controlled Fusio

Resultados de pesquisa obtidos na cultura do algodão nos cerrados da região Meio-Norte do Brasil no período de 1999 a 2008.

O objetivo deste trabalho é informar aos produtores de algodão da região Meio-Norte do Brasil sobre os resultados de pesquisa obtidos no período de 1999 a 2008. Nesse período foram conduzidos 91 experimentos de avaliação de genótipos visando a introdução da cultura algodoeira como uma alternativa para a rotação com as culturas de soja e milho. No Piauí, os trabalhos de pesquisa foram realizados nos municípios de Teresina, Bom Jesus, Uruçuí, Palmeira do Piauí e Baixa Grande do Ribeiro e, no Maranhão, nos municípios de Tasso Fragoso, Sambaíba, São Raimundo das Mangabeiras, Chapadinha, Brejo, Anapurus e Mata Roma. A amplitude para produtividade média de algodão em caroço variou de 2.628 kg ha-1 a 3.598 kg/ha-1 , no Piauí e, de 2.522 kg/ha-1 a 3.360 kg/ha-1, no Maranhão. No Piauí, os municípios de Baixa Grande do Ribeiro e Uruçuí apresentaram as maiores produtividades com uma amplitude de variação de 3.254 kg/ha-1 a 4.356 kg/ha-1 e 2.730 kg/ha-1 a 3.419 kg/ha-1, respectivamente. No Maranhão as melhores produtividades ocorreram nos municípios de Tasso Fragoso com uma amplitude de variação de 2.751 kg/ha-1 a 4.236 kg/ha-1 e, em São Raimundo das Mangabeiras com uma amplitude de variação de 3.313 kg/ha-1 a 3.943 kg/ha-1

Five-Dimensional QED, Muon Pair Production and Correction to the Coulomb Potential

We consider QED in five dimensions in a configuration where matter is localized on a 3-brane while foton propagates in the bulk. The idea is to investigate the effects of the Kaluza-Klein modes of the photon in the relativistic regime, but in low energy, and in the nonrelativistic regime. In the relativistic regime, we calculate the cross section for the reaction $e^+ + e^- \to \mu^+ + \mu^-$. We compare our theoretical result with a precise measurement of this cross section at $\sqrt{s}=57.77$ GeV. As result, we extract a lower bound on the size of the extra dimension. In the nonrelativistic regime, we derive the contribution for the Coulomb potential due to the whole tower of the Kaluza-Klein excited modes of the photon. We use the modified potential to calculate the Rutherford scattering differential cross section.Comment: minor changes, three new refs. added, to appear in IJMP