Systems Research Institute

About: Systems Research Institute is a facility organization based out in Warsaw, Poland. It is known for research contribution in the topics: Population & Fuzzy logic. The organization has 1384 authors who have published 2350 publications receiving 104534 citations.

Making Nonmagnetic Semiconductors Ferromagnetic

Abstract: REVIEW Semiconductor devices generally take advantage of the charge of electrons, whereas magnetic materials are used for recording information involving electron spin. To make use of both charge and spin of electrons in semiconductors, a high concentration of magnetic elements can be introduced in nonmagnetic III-V semiconductors currently in use for devices. Low solubility of magnetic elements was overcome by low-temperature nonequilibrium molecular beam epitaxial growth, and ferromagnetic (Ga,Mn)As was realized. Magnetotransport measurements revealed that the magnetic transition temperature can be as high as 110 kelvin. The origin of the ferromagnetic interaction is discussed. Multilayer heterostructures including resonant tunneling diodes (RTDs) have also successfully been fabricated. The magnetic coupling between two ferromagnetic (Ga,Mn)As films separated by a nonmagnetic layer indicated the critical role of the holes in the magnetic coupling. The magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin filtering in RTDs, shows the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.

Conceptual Structures: Information Processing in Mind and Machine

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Electrical spin injection in a ferromagnetic semiconductor heterostructure

Abstract: Conventional electronics is based on the manipulation of electronic charge. An intriguing alternative is the field of ‘spintronics’, wherein the classical manipulation of electronic spin in semiconductor devices gives rise to the possibility of reading and writing non-volatile information through magnetism1,2. Moreover, the ability to preserve coherent spin states in conventional semiconductors3 and quantum dots4 may eventually enable quantum computing in the solid state5,6. Recent studies have shown that optically excited electron spins can retain their coherence over distances exceeding 100 micrometres (ref. 7). But to inject spin-polarized carriers electrically remains a formidable challenge8,9. Here we report the fabrication of all-semiconductor, light-emitting spintronic devices using III–V heterostructures based on gallium arsenide. Electrical spin injection into a non-magnetic semiconductor is achieved (in zero magnetic field) using a p-type ferromagnetic semiconductor10 as the spin polarizer. Spin polarization of the injected holes is determined directly from the polarization of the emitted electroluminescence following the recombination of the holes with the injected (unpolarized) electrons.

Genetic variation in IL28B and spontaneous clearance of hepatitis C virus

Abstract: Hepatitis C virus (HCV) infection is the most common blood-borne infection in the United States, with estimates of 4 million HCV-infected individuals in the United States and 170 million worldwide. Most (70-80%) HCV infections persist and about 30% of individuals with persistent infection develop chronic liver disease, including cirrhosis and hepatocellular carcinoma. Epidemiological, viral and host factors have been associated with the differences in HCV clearance or persistence, and studies have demonstrated that a strong host immune response against HCV favours viral clearance. Thus, variation in genes involved in the immune response may contribute to the ability to clear the virus. In a recent genome-wide association study, a single nucleotide polymorphism (rs12979860) 3 kilobases upstream of the IL28B gene, which encodes the type III interferon IFN-3, was shown to associate strongly with more than a twofold difference in response to HCV drug treatment. To determine the potential effect of rs12979860 variation on outcome to HCV infection in a natural history setting, we genotyped this variant in HCV cohorts comprised of individuals who spontaneously cleared the virus (n = 388) or had persistent infection (n = 620). We show that the C/C genotype strongly enhances resolution of HCV infection among individuals of both European and African ancestry. To our knowledge, this is the strongest and most significant genetic effect associated with natural clearance of HCV, and these results implicate a primary role for IL28B in resolution of HCV infection.

Electric-field control of ferromagnetism

Abstract: It is often assumed that it is not possible to alter the properties of magnetic materials once they have been prepared and put into use. For example, although magnetic materials are used in information technology to store trillions of bits (in the form of magnetization directions established by applying external magnetic fields), the properties of the magnetic medium itself remain unchanged on magnetization reversal. The ability to externally control the properties of magnetic materials would be highly desirable from fundamental and technological viewpoints, particularly in view of recent developments in magnetoelectronics and spintronics. In semiconductors, the conductivity can be varied by applying an electric field, but the electrical manipulation of magnetism has proved elusive. Here we demonstrate electric-field control of ferromagnetism in a thin-film semiconducting alloy, using an insulating-gate field-effect transistor structure. By applying electric fields, we are able to vary isothermally and reversibly the transition temperature of hole-induced ferromagnetism.