Radically Rethinking Agriculture for the 21st Century Fedoroff, N. V.; Battisti, D. S.; Beachy, R. N. ...
Science (American Association for the Advancement of Science),
02/2010, Letnik:
327, Številka:
5967
Journal Article
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Population growth, arable land and fresh water limits, and climate change have profound implications for the ability of agriculture to meet this century's demands for food, feed, fiber, and fuel ...while reducing the environmental impact of their production. Success depends on the acceptance and use of contemporary molecular techniques, as well as the increasing development of farming systems that use saline water and integrate nutrient flows.
This paper describes the Magnetic Electron Ion Spectrometer (MagEIS) instruments aboard the RBSP spacecraft from an instrumentation and engineering point of view. There are four magnetic ...spectrometers aboard each of the two spacecraft, one low-energy unit (20–240 keV), two medium-energy units (80–1200 keV), and a high-energy unit (800–4800 keV). The high unit also contains a proton telescope (55 keV–20 MeV).
The magnetic spectrometers focus electrons within a selected energy pass band upon a focal plane of several silicon detectors where pulse-height analysis is used to determine if the energy of the incident electron is appropriate for the electron momentum selected by the magnet. Thus each event is a two-parameter analysis, an approach leading to a greatly reduced background.
The physics of these instruments are described in detail followed by the engineering implementation. The data outputs are described, and examples of the calibration results and early flight data presented.
The temperature dependency of kinetic parameters in p-PbTe and p-CdTe thin films formed on glass substrates has been investigated. The surface mobility of current carriers in PbTe films was computed ...as a function of temperature under the assumption of diffuse scattering of charge carriers. The mechanisms of intergranular current carrier transfer related with thermoelectronic emission are established. The role of surface scattering and intergranular boundaries in thin films of lead and cadmium tellurides is addressed.
Abstract
The realization of hybrid superconductor–semiconductor quantum devices, in particular a topological qubit, calls for advanced techniques to readily and reproducibly engineer induced ...superconductivity in semiconductor nanowires. Here, we introduce an on-chip fabrication paradigm based on shadow walls that offers substantial advances in device quality and reproducibility. It allows for the implementation of hybrid quantum devices and ultimately topological qubits while eliminating fabrication steps such as lithography and etching. This is critical to preserve the integrity and homogeneity of the fragile hybrid interfaces. The approach simplifies the reproducible fabrication of devices with a hard induced superconducting gap and ballistic normal-/superconductor junctions. Large gate-tunable supercurrents and high-order multiple Andreev reflections manifest the exceptional coherence of the resulting nanowire Josephson junctions. Our approach enables the realization of 3-terminal devices, where zero-bias conductance peaks emerge in a magnetic field concurrently at both boundaries of the one-dimensional hybrids.
The proximity effect in semiconductor-superconductor nanowires is expected to generate an induced gap in the semiconductor. The magnitude of this induced gap, together with the semiconductor ...properties like spin-orbit coupling and g-factor, depends on the coupling between the materials. It is predicted that this coupling can be adjusted through the use of electric fields. We study this phenomenon in InSb/Al/Pt hybrids using nonlocal spectroscopy. We show that these hybrids can be tuned such that the semiconductor and superconductor are strongly coupled. In this case, the induced gap is similar to the superconducting gap in the Al/Pt shell and closes only at high magnetic fields. In contrast, the coupling can be suppressed which leads to a strong reduction of the induced gap and critical magnetic field. At the crossover between the strong-coupling and weak-coupling regimes, we observe the closing and reopening of the induced gap in the bulk of a nanowire. Contrary to expectations, it is not accompanied by the formation of zero-bias peaks in the local conductance spectra. As a result, this cannot be attributed conclusively to the anticipated topological phase transition and we discuss possible alternative explanations.
In superconducting quantum circuits, aluminum is one of the most widely used materials. It is currently also the superconductor of choice for the development of topological qubits. However, ...aluminum‐based devices suffer from poor magnetic field compatibility. Herein, this limitation is resolved by showing that adatoms of heavy elements (e.g., platinum) increase the critical field of thin aluminum films by more than a factor of two. Using tunnel junctions, it is shown that the increased field resilience originates from spin‐orbit scattering introduced by Pt. This property is exploited in the context of the superconducting proximity effect in semiconductor–superconductor hybrids, where it is shown that InSb nanowires strongly coupled to Al/Pt films can maintain superconductivity up to 7 T. The two‐electron charging effect is shown to be robust against the presence of heavy adatoms. Additionally, non‐local spectroscopy is used in a three‐terminal geometry to probe the bulk of hybrid devices, showing that it remains free of sub‐gap states. Finally, it is demonstrated that proximitized semiconductor states maintain their ability to Zeeman‐split in an applied magnetic field. Combined with the chemical stability and well‐known fabrication routes of aluminum, Al/Pt emerges as the natural successor to Al‐based systems and is a compelling alternative to other superconductors, whenever high‐field resilience is required.
In superconducting quantum circuits, aluminum is one of the most widely used materials. Aluminum‐based devices suffer from poor magnetic field compatibility. In this article, this limitation is resolved by showing that adatoms of heavy elements (e.g., platinum) increase the critical field of thin aluminum films by more than a factor of two.
Abstract
Semiconductor nanowires coupled to superconductors can host Andreev bound states with distinct spin and parity, including a spin-zero state with an even number of electrons and a spin-1/2 ...state with odd-parity. Considering the difference in spin of the even and odd states, spin-filtered measurements can reveal the underlying ground state. To directly measure the spin of single-electron excitations, we probe an Andreev bound state using a spin-polarized quantum dot that acts as a bipolar spin filter, in combination with a non-polarized tunnel junction in a three-terminal circuit. We observe a spin-polarized excitation spectrum of the Andreev bound state, which can be fully spin-polarized, despite strong spin-orbit interaction in the InSb nanowires. Decoupling the hybrid from the normal lead causes a current blockade, by trapping the Andreev bound state in an excited state. Spin-polarized spectroscopy of hybrid nanowire devices, as demonstrated here, is proposed as an experimental tool to support the observation of topological superconductivity.
A modified surface was obtained on wide-gap II-VI compounds. The methods of thermal annealing for cadmium chalcogenides and chemical etching for the first time obtained heterolayers of atypical ...hexagonal modification of α-ZnSe have been improved. AFM topograms of surface nanostructures have been investigated and comprehensive studies of optical and luminescent properties have been carried out. The emission spectra were determined in the photon energy range 1.4-3.6 eV and the important role of recombination processes in the formation of the A band in the edge region was established. The dominant role of quantum-dimensional processes in the formation of the obtained B band of intense radiation in a wide spectral region of the visible and ultraviolet ranges has been established.
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