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

Domain wall scattering in an interacting one-dimensional electron gas

We study the transport in a Luttinger liquid coupled to a magnetic chain containing a Bloch domain wall. We compute the leading correction to the adiabatic limit of a long domain wall, which causes no scattering. We show that the problem is reminiscent of an impurity in a Luttinger liquid, but with a different dependence on the interaction parameters due to spin-flip scattering. For repulsive interactions, we find that the domain wall resistance diverges with decreasing temperature. This may be relevant for the design of one-dimensional systems with large magnetoresistance at low temperatures.Comment: 4 pages, 1 figur

Massive Black Hole Binary Systems in Hierarchical Scenario of Structure Formation

The hierarchical scenario of structure formation describes how objects like galaxies and galaxy clusters are formed by mergers of small objects. In this scenario, mergers of galaxies can lead to the formation of massive black hole (MBH) binary systems. On the other hand, the merger of two MBH could produce a gravitational wave signal detectable, in principle, by the Laser Interferometer Space Antenna (LISA). In the present work, we use the Press-Schechter formalism, and its extension, to describe the merger rate of haloes which contain massive black holes. Here, we do not study the gravitational wave emission of these systems. However, we present an initial study to determine the number of systems formed via mergers that could permit, in a future extension of this work, the calculation of the signature in gravitational waves of these systems.Comment: to match the published version in International Journal of Modern Physics

Magnetically-controlled impurities in quantum wires with strong Rashba coupling

We investigate the effect of strong spin-orbit interaction on the electronic transport through non-magnetic impurities in one-dimensional systems. When a perpendicular magnetic field is applied, the electron spin polarization becomes momentum-dependent and spin-flip scattering appears, to first order in the applied field, in addition to the usual potential scattering. We analyze a situation in which, by tuning the Fermi level and the Rashba coupling, the magnetic field can suppress the potential scattering. This mechanism should give rise to a significant negative magnetoresistance in the limit of large barriers.Comment: 4 pages, 2 figure

Correlation amplitude and entanglement entropy in random spin chains

Using strong-disorder renormalization group, numerical exact diagonalization, and quantum Monte Carlo methods, we revisit the random antiferromagnetic XXZ spin-1/2 chain focusing on the long-length and ground-state behavior of the average time-independent spin-spin correlation function C(l)=\upsilon l^{-\eta}. In addition to the well-known universal (disorder-independent) power-law exponent \eta=2, we find interesting universal features displayed by the prefactor \upsilon=\upsilon_o/3, if l is odd, and \upsilon=\upsilon_e/3, otherwise. Although \upsilon_o and \upsilon_e are nonuniversal (disorder dependent) and distinct in magnitude, the combination \upsilon_o + \upsilon_e = -1/4 is universal if C is computed along the symmetric (longitudinal) axis. The origin of the nonuniversalities of the prefactors is discussed in the renormalization-group framework where a solvable toy model is considered. Moreover, we relate the average correlation function with the average entanglement entropy, whose amplitude has been recently shown to be universal. The nonuniversalities of the prefactors are shown to contribute only to surface terms of the entropy. Finally, we discuss the experimental relevance of our results by computing the structure factor whose scaling properties, interestingly, depend on the correlation prefactors.Comment: v1: 16 pages, 15 figures; v2: 17 pages, improved discussions and statistics, references added, published versio

Dimerization induced by the RKKY interaction

We report the presence of spin dimerization in the ground state of the one dimensional Kondo lattice model at quarter filling. The emergence of this new phase of the Kondo lattice can be traced to the form of the RKKY interaction between the localized moments and provides the first example of dimerization induced indirectly by itinerant electrons. We propose this dimer ordering as the driving mechanism of the spin-Peierls phase observed in the quasi-one-dimensional organic compounds (Per)$_{2}$M(mnt)$_{2}$ (M=Pt, Pd). Moreover, this suggests that a richer phase diagram than the Doniach paradigm may be needed to accommodate the physics of heavy fermion materials.Comment: 4 pages, 6 figure

Science and the Green Revolution in the Brazilian Amazon: The Establishment of Embrapa during of the Civilian-Military Dictatorship and the Emergence of Environmental Movements (1972-1991)

The Empresa Brasileira de Pesquisa Agropecuária (Brazilian Agricultural Research Corporation), known by the acronym Embrapa, was established in 1972 under Brazil’s civilian-military dictatorship with the purpose of fostering agricultural modernization through the incorporation of the Green Revolution’s technology package, which included reliance on chemical inputs and high-yielding hybrid seeds and the mechanization of production. This article explores the context in which the agency was established and its scientific research agenda for Brazilian agriculture, while also examining both the influence of emerging environmentalist movements on discussions of the economic exploitation of the Amazon as well as the agency’s profile during the period of redemocratization in Brazil. The focus of our analysis is on the agency branch known as the Humid Tropics Agricultural Research Center (Centro de Pesquisa Agropecuária do Trópico Úmido, or CPATU), which opened in Belém, Pará, in 1975. The text follows the path of the CPATU through 1991, when it became the Eastern Amazon Agroforestry Research Center (Centro de Pesquisa Agroflorestal da Amazônia Oriental), now Embrapa Eastern Amazon (Embrapa Amazônia Oriental).The Empresa Brasileira de Pesquisa Agropecuária (Brazilian Agricultural Research Corporation), known by the acronym Embrapa, was established in 1972 under Brazil’s civilian-military dictatorship with the purpose of fostering agricultural modernization through the incorporation of the Green Revolution’s technology package, which included reliance on chemical inputs and high-yielding hybrid seeds and the mechanization of production. This article explores the context in which the agency was established and its scientific research agenda for Brazilian agriculture, while also examining both the influence of emerging environmentalist movements on discussions of the economic exploitation of the Amazon as well as the agency’s profile during the period of redemocratization in Brazil. The focus of our analysis is on the agency branch known as the Humid Tropics Agricultural Research Center (Centro de Pesquisa Agropecuária do Trópico Úmido, or CPATU), which opened in Belém, Pará, in 1975. The text follows the path of the CPATU through 1991, when it became the Eastern Amazon Agroforestry Research Center (Centro de Pesquisa Agroflorestal da Amazônia Oriental), now Embrapa Eastern Amazon (Embrapa Amazônia Oriental).The Empresa Brasileira de Pesquisa Agropecuária (Brazilian Agricultural Research Corporation), known by the acronym Embrapa, was established in 1972 under Brazil’s civilian-military dictatorship with the purpose of fostering agricultural modernization through the incorporation of the Green Revolution’s technology package, which included reliance on chemical inputs and high-yielding hybrid seeds and the mechanization of production. This article explores the context in which the agency was established and its scientific research agenda for Brazilian agriculture, while also examining both the influence of emerging environmentalist movements on discussions of the economic exploitation of the Amazon as well as the agency’s profile during the period of redemocratization in Brazil. The focus of our analysis is on the agency branch known as the Humid Tropics Agricultural Research Center (Centro de Pesquisa Agropecuária do Trópico Úmido, or CPATU), which opened in Belém, Pará, in 1975. The text follows the path of the CPATU through 1991, when it became the Eastern Amazon Agroforestry Research Center (Centro de Pesquisa Agroflorestal da Amazônia Oriental), now Embrapa Eastern Amazon (Embrapa Amazônia Oriental)

Edge magnetization and spin transport in an SU(2)-symmetric Kitaev spin liquid

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOMEC - MINISTÉRIO DA EDUCAÇÃOMCTIC - MINISTÉRIO DA CIÊNCIA, TECNOLOGIA, INOVAÇÕES E COMUNICAÇÕESCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOWe investigate the edge magnetism and the spin transport properties of an SU(2)-symmetric Kitaev spin liquid (KSL) model put forward by Yao and Lee [Phys. Rev. Lett. 107, 087205 (2011)] on the honeycomb lattice. In this model, the spin degrees of freedom fractionalize into a Z(2) static gauge field and three species of either gapless (Dirac) or gapped (chiral) Majorana fermionic excitations. We find that, when a magnetic field is applied on a zigzag edge, the Dirac KSL exhibits a nonlocal magnetization associated with the existence of zero-energy edge modes. The application of a spin bias V = mu(up arrow) - mu(down arrow) y at the interface of the spin system with a normal metal produces a spin current into the KSL, which depends as a power law on V, in the zero-temperature limit, for both Dirac and chiral KSLs, but with different exponents. Lastly, we study the longitudinal spin Seebeck effect, in which a spin current is driven by the combined action of a magnetic field perpendicular to the plane of the honeycomb lattice and a thermal gradient at the interface of the KSL with a metal. Our results suggest that edge magnetization and spin transport can be used to probe the existence of charge-neutral edge states in quantum spin liquids.9815112FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOMEC - MINISTÉRIO DA EDUCAÇÃOMCTIC - MINISTÉRIO DA CIÊNCIA, TECNOLOGIA, INOVAÇÕES E COMUNICAÇÕESCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOMEC - MINISTÉRIO DA EDUCAÇÃOMCTIC - MINISTÉRIO DA CIÊNCIA, TECNOLOGIA, INOVAÇÕES E COMUNICAÇÕESCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO2016/05069-7sem informaçãosem informação405584/2016-

Comportamento de seis linhagens de café (Coffea arabica L.) em condições de sombreamento e a pleno sol no Estado do Acre, Brasil.

Este trabalho teve como objetivo indicar uma linhagem de café (Coffea arabica L.), adaptada ao cultivo sob sombra, nas condições edafoclimáticas de Rio Branco, Acre. Foi comparado o desempenho do cafeeiro sombreado com o plantio a pleno sol, através da avaliação do crescimento, vigor vegetativo e produtividade de seis linhagens. O delineamento experimental foi de blocos ao acaso com parcelas sub-divididas, com cinco repetições, sendo a condição de luminosidade (sombreado e a pleno sol) colocada nas parcelas e as linhagens nas subparcelas. As li-nhagens foram plantadas em março de 1993, no es-paçamento de 3m x 2m (2 mudas por cova). Para o sombreamento definitivo, utilizaram-se ingazeiros (Inga edulis Mart) no espaçamento de 12m x 12m, e no sombreamento temporário, bananeiras (Musa sp.) a 6m x 2m. Os resultados das duas primeiras colheitas de café, realizadas em 1995 e 1996, mostraram que o rendimento a pleno sol foi significativamente supe-rior, com diferenças significativas entre as linhagens. Nas parcelas mantidas sob sombra, não houve diferenças significativas, o que pode indicar que o ambiente foi muito adverso para as linhagens mos-trarem seu potencial genético produtivo. As linhagens mais produtivas foram: 'EP57-C260' (germoplasma Catuaí Sh1), 'IAC 1669-20' (germoplasma Sarchimor) e 'IAC 2077-2-5-62' (germoplasma Catuaí Amarelo), mostrando-se promissoras para recomenda-ção local, todas com rendimento superior a 1300 kg de café em grãos/ha