2,487 research outputs found
Effects of next-nearest-neighbor hopping on the electronic structure of cuprates
Photoemission spectra of underdoped and lightly-doped
BiPbSrCa{\it R}CuO ( Pr, Er)
(BSCCO) have been measured and compared with those of LaSrCuO
(LSCO). The lower-Hubbard band of the insulating BSCCO, like
CaCuOCl, shows a stronger dispersion than LaCuO from () to (). The flat band at () is found generally deeper in BSCCO. These observations
together with the Fermi-surface shapes and the chemical potential shifts
indicate that the next-nearest-neighbor hopping of the
single-band model is larger in BSCCO than in LSCO and that
rather than the super-exchange influences the pseudogap energy scale.Comment: 5 pages,4 figures, 1 tabl
Highly sensitive InGaAs=InAlAs quantum wire photo-FET
An InGaAs=InAlAs quantum wire photo-FET has been fabricated on a V-grooved (311) InP substrate by atomic hydrogen assisted molecular beam epitaxy. The room-temperature photosensitivity of the quantum wire photo-FET reached 350 kA=W near a wavelength of 700 nm at a drain-source voltage of 1 V. Introduction: The pin diode is the simplest of the commercially available photodetectors in terms of device structure and is suitable for application to a detector array. However, its sensitivity is limited to about 1 A=W, which is the quantum efficiency of the photo-absorption material. In such a case, the detection limit is determined by the additional electronic noise induced by the current amplifier. In contrast, an avalanche photodiode (APD) and a photo-multiplier (PMT) have higher sensitivity because of their amplification mechanism, but they are not very suitable for multi-pixel arrays because of their inferior uniformity and higher bias voltage. The bias voltages of an APD (1 kV) may easily damage a silicon charge amplifier within the same package if the element breaks down. A phototransistor is a good candidate for a highly sensitive photodetector. In a metal oxide semiconductor field effect transistor (MOSFET), photo-generated carriers are accumulated underneath the gate region and modulate the majority current. This device is called a photo-MOSFET and it is widely used for optically isolated relays and image sensors. Compound semiconductor materials are essential if we are to extend the spectral range and sensitivity of photodetectors by flexibly designing the bandgap profile and achieving high carrier mobility. It is reported that high electron mobility transistors (HEMTs) have a responsivity of about 3 kA=W as a photodetecto
Cross-Field Plasma Acceleration and Potential Formation Induced by Electromagnetic Waves in a Relativistic Magnetized Plasma
Abstract It has been proved theoretically that particle acceleration along and across a magnetic field and electric field across a magnetic field can be induced by nonlinear Landau damping of almost perpendicularly propagating electrostatic waves in a relativistic magnetized plasma
Avaliação da avifauna em sistemas agroflorestais com dendê (Elaeis guianeensis) no municÃpio de Tomé-Açu (PA).
È apresentada uma comparação entre a composição da avifauna de sistemas agroflorestais (SAF) com dendê, copoeiras e uma monocultura de dendê ao longo de dois anos no intuito de relatar a funcionalidade dos SAFs na manutenção de aves amazônicas. Foram registradas 196 espécies, destas 88 encontradas nos SAFs, 120 na capoeira e 63 na monocultura. Foi observada a ausência de espécies florestais das famÃlias, Thamnophilidae, Furnaridae e Tyrannidae no SAF e na monocultura de dendê, presentes na capoeira. O Ãndice de similaridade de Morisita mostra que os SAFs se assemelham mais à s monoculturas do que à s capoeiras, possivelmente devido ao tempo recente de plantio, onde os SAFs ainda não apresentam uma estrutura florestal mais complexa com sub-bosque e dossel. Foi observado um aumento na riqueza de espécies frutÃvoras e nectarÃvoras e na diversidade dos SAFs, possivelmente refletindo o contÃnuo desenvolvimento e estruturação deste sistema. Os resultados apresentados mostram que apesar de os SAFs apresentarem uma comunidade de aves em geral distinta da comunidade encontrada nas capoeiras, estas apresentam Ãndices de diversidade e riqueza de espécies semelhantes. A monocultura de dendê apresentou a menor riqueza e Ãndices de diversidade, além de apresentar principalmente espécies insetÃvoras, onÃvoras e granÃvoras na composição de sua avifauna, configurando um ambiente pouco diverso na estrutura da vegetação. Sistemas agroflorestais de dendê podem vir a contribuir na manutenção da diversidade local de aves florestais amazônicas, contudo os resultados apontam a necessidade de mais tempo para um melhor desenvolvimento do sistema.Editores técnicos: Roberto Porro, Milton Kanashiro, Maria do Socorro Gonçalves Ferreira, Leila Sobral Sampaio e Gladys Ferreira de Sousa
Measuring Temperature Gradients over Nanometer Length Scales
When a quantum dot is subjected to a thermal gradient, the temperature of
electrons entering the dot can be determined from the dot's thermocurrent if
the conductance spectrum and background temperature are known. We demonstrate
this technique by measuring the temperature difference across a 15 nm quantum
dot embedded in a nanowire. This technique can be used when the dot's energy
states are separated by many kT and will enable future quantitative
investigations of electron-phonon interaction, nonlinear thermoelectric
effects, and the effciency of thermoelectric energy conversion in quantum dots.Comment: 6 pages, 5 figure
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