Quantum field theory solution for a short-range interacting SO(3) quantum spin-glass

We study the quenched disordered magnetic system, which is obtained from the 2D SO(3) quantum Heisenberg model, on a square lattice, with nearest neighbors interaction, by taking a Gaussian random distribution of couplings centered in an antiferromagnetic coupling, $\bar J>0$ and with a width $\Delta J$. Using coherent spin states we can integrate over the random variables and map the system onto a field theory, which is a generalization of the SO(3) nonlinear sigma model with different flavors corresponding to the replicas, coupling parameter proportional to $\bar J$ and having a quartic spin interaction proportional to the disorder ($\Delta J$). After deriving the CP$^1$ version of the system, we perform a calculation of the free energy density in the limit of zero replicas, which fully includes the quantum fluctuations of the CP$^1$ fields $z_i$. We, thereby obtain the phase diagram of the system in terms of ($T, \bar J, \Delta J$). This presents an ordered antiferromagnetic (AF) phase, a paramagnetic (PM) phase and a spin-glass (SG) phase. A critical curve separating the PM and SG phases ends at a quantum critical point located between the AF and SG phases, at T=0. The Edwards-Anderson order parameter, as well as the magnetic susceptibilities are explicitly obtained in each of the three phases as a function of the three control parameters. The magnetic susceptibilities show a Curie-type behavior at high temperatures and exhibit a clear cusp, characteristic of the SG transition, at the transition line. The thermodynamic stability of the phases is investigated by a careful analysis of the Hessian matrix of the free energy. We show that all principal minors of the Hessian are positive in the limit of zero replicas, implying in particular that the SG phase is stable.Comment: To appear in Nucl. Phys B [FS], 16 pages, 6 figure

Leigh Syndrome with Atypical Cerebellum Imaging Features

info:eu-repo/semantics/publishedVersio

A T1-Hypointense Intracranial Dermoid Cyst

info:eu-repo/semantics/publishedVersio

Stable Mean Field Solution of a Short-Range Interacting SO(3) Quantum Heisenberg Spin-Glass

We present a mean-field solution for a quantum, short-range interacting, disordered, SO(3) Heisenberg spin model, in which the Gaussian distribution of couplings is centered in an AF coupling $\bar J>0$, and which, for weak disorder, can be treated as a perturbation of the pure AF Heisenberg system. The phase diagram contains, apart from a N\'eel phase at T=0, spin-glass and paramagnetic phases whose thermodynamic stability is demonstrated by an analysis of the Hessian matrix of the free-energy. The magnetic susceptibilities exhibit the typical cusp of a spin-glass transition.Comment: 4 page

Velocidade de adoção de variedades de mandioca no bioma Caatinga recomendadas pela Embrapa.

Esta Circular Técnica tem por objetivo calcular a velocidade de adoção, no bioma Caatinga, de 14 variedades de mandioca recomendadas pela Embrapa Mandioca e Fruticultura, no período de 1999 a 2008.bitstream/item/122503/1/CircularTecnica-113-C-A-AP-15-04-2015.pd

Padronização do extrato de Ruta graveolens L. e avaliação da sua atividade em Magnaporthe oryzae.

O objetivo deste estudo foi padronizar o extrato vegetal líquido de R. graveolens L. e avaliar seu potencial para o controle da brusone em arroz.Apresentação oral - Pós-graduação