Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green's functions

Using non-equilibrium Green functions we calculate the spin-polarized current and shot noise in a ferromagnet--quantum-dot--ferromagnet (FM-QD-FM) system. Both parallel (P) and antiparallel (AP) magnetic configurations are considered. Coulomb interaction and coherent spin-flip (similar to a transverse magnetic field) are taken into account within the dot. We find that the interplay between Coulomb interaction and spin accumulation in the dot can result in a bias-dependent current polarization $\wp$. In particular, $\wp$ can be suppressed in the P alignment and enhanced in the AP case depending on the bias voltage. The coherent spin-flip can also result in a switch of the current polarization from the emitter to the collector lead. Interestingly, for a particular set of parameters it is possible to have a polarized current in the collector and an unpolarized current in the emitter lead. We also found a suppression of the Fano factor to values well below 0.5.Comment: Published version. 13 pages, 7 figure

Mesoscopic Kondo effect of a quantum dot embedded in an Aharonov-Bohm ring with intradot spin-flip scattering

We study the Kondo effect in a quantum dot embedded in a mesoscopic ring taking into account intradot spin-flip scattering $R$. Based on the finite-$U$ slave-boson mean-field approach, we find that the Kondo peak in the density of states is split into two peaks by this coherent spin-flip transition, which is responsible for some interesting features of the Kondo-assisted persistent current circulating the ring: (1) strong suppression and crossover to a sine function form with increasing $R$; (2) appearance of a "hump" in the $R$-dependent behavior for odd parity. $R$-induced reverse of the persistent current direction is also observed for odd parity.Comment: 7 pages,6 figures, to be published by Europhys. Let

Bose-Einstein Condensation Temperature of Homogenous Weakly Interacting Bose Gas in Variational Perturbation Theory Through Six Loops

We compute the shift of the transition temperature for a homogenous weakly interacting Bose gas in leading order in the scattering length a for given particle density n. Using variational perturbation theory through six loops in a classical three-dimensional scalar field theory, we obtain Delta T_c/T_c = 1.25+/-0.13 a n^(1/3), in agreement with recent Monte-Carlo results.Comment: 4 pages; omega' corrected: final result changes slightly to 1.25+/-0.13; references added; several minor change

Low-cost thermal imager for plant phenotyping.

This work uses a Flir Lepton 3 longwave infrared imager integrated with a Raspberry Pi computer to produce thermal images of crops. The longwave infrared sensor can detect the thermal radiation emitted by objects near room temperature and then determine its temperature.Editores: Paulo Sérgio de Paula Herrmann Junior, Paulino Ribeiro Villas Boas

Estratégias de cruzamentos para produção de caprinos e ovinos de corte: uma experiência da Emepa.

A diversidade de raças de ovinos e caprinos existentes no Brasil é um valioso recurso para o desenvolvimento da caprino-ovinocultura. Sistemas de cruzamentos utilizam-se da diversidade de raça para aumentar produtividade quando comparada aos rebanhos puros. Sistemas de cruzamentos variam em complexidade de manejo e da utilização dos efeitos benéficos, devido os cordeiros e ovelhas mestiças. A eficiência de produção de carne é maximizada em sistemas de cruzamentos terminais através do uso de raças paternas especializadas, para complementar características das ovelhas e/ou cabras mestiças. Este artigo tem como objetivo discutir alguns aspectos relacionados com a diversidade de raça, efeitos de heterose, complementaridade e vantagens e desvantagens de sistemas de cruzamentos terminais, bem como resultados de diversos trabalhos de cruzamentos em caprinos e ovinos de corte realizados, nos últimos anos, pela Emepa e parceiros

Frequency-Dependent Current Noise through Quantum-Dot Spin Valves

We study frequency-dependent current noise through a single-level quantum dot connected to ferromagnetic leads with non-collinear magnetization. We propose to use the frequency-dependent Fano factor as a tool to detect single-spin dynamics in the quantum dot. Spin precession due to an external magnetic and/or a many-body exchange field affects the Fano factor of the system in two ways. First, the tendency towards spin-selective bunching of the transmitted electrons is suppressed, which gives rise to a reduction of the low-frequency noise. Second, the noise spectrum displays a resonance at the Larmor frequency, whose lineshape depends on the relative angle of the leads' magnetizations.Comment: 12 pages, 15 figure

Low-cost thermal field mapping.

This project is originally designed to be used in rice genetic enhancement fields, but it can be used for other purposes, for example, to verify if any part of the tillage has a disease, when comparing the thermal signature of the species with the thermal map.Editores: Paulo Sérgio de Paula Herrmann Junior, Paulino Ribeiro Villas Boas