This review describes a new paradigm of electronics based on the spin degree of freedom of the electron. Either adding the spin degree of freedom to conventional charge-based electronic devices or using the spin alone has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices. To successfully incorporate spins into existing semiconductor technology, one has to resolve technical issues such as efficient injection, transport, control and manipulation, and detection of spin polarization as well as spin-polarized currents. Recent advances in new materials engineering hold the promise of realizing spintronic devices in the near future. We review the current state of the spin-based devices, efforts in new materials fabrication, issues in spin transport, and optical spin manipulation.

http://science.sciencemag.org/content/sci/294/5546/1488.full.pdf

Spintronics: a spin-based electronics vision for the future.

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

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Spintronics: Fundamentals and applications

We propose an electron wave analog of the electro‐optic light modulator. The current modulation in the proposed structure arises from spin precession due to the spin‐orbit coupling in narrow‐gap semiconductors, while magnetized contacts are used to preferentially inject and detect specific spin orientations. This structure may exhibit significant current modulation despite multiple modes, elevated temperatures, or a large applied bias.

Electronic analog of the electro‐optic modulator

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

/pdf/science-and-technology-roadmap-for-graphene-related-two-4q9m7czlkc.pdf

Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

Electrons have a charge and a spin, but until recently these were considered separately. In classical electronics, charges are moved by electric fields to transmit information and are stored in a capacitor to save it. In magnetic recording, magnetic fields have been used to read or write the information stored on the magnetization, which 'measures' the local orientation of spins in ferromagnets. The picture started to change in 1988, when the discovery of giant magnetoresistance opened the way to efficient control of charge transport through magnetization. The recent expansion of hard-disk recording owes much to this development. We are starting to see a new paradigm where magnetization dynamics and charge currents act on each other in nanostructured artificial materials. Ultimately, 'spin currents' could even replace charge currents for the transfer and treatment of information, allowing faster, low-energy operations: spin electronics is on its way.

/pdf/the-emergence-of-spin-electronics-in-data-storage-1vrnm5549k.pdf

The emergence of spin electronics in data storage

The splitting in zero magnetic field between the up- and down-spin electrons in a two-dimensional electron gas is obtained for a series of three different ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}/{\mathrm{In}}_{0.52}{\mathrm{Al}}_{0.48}\mathrm{As}$ modulation-doped heterostructures with high electron densities [${n}_{s}\ensuremath{\sim}(1.5\ensuremath{-}1.8)\ifmmode\times\else\texttimes\fi{}{10}^{12}$ ${\mathrm{cm}}^{\ensuremath{-}2}$]. We have observed a characteristic beating modulation in the amplitude of the Shubnikov-de Haas oscillations in this system and up to six nodes have been measured in the Shubnikov-de Haas data for magnetic fields in the range $0.15 \mathrm{T}lBl1.0 \mathrm{T}$. Analysis of these data indicates that one subband is primarily occupied and the two beating frequencies arise from a spin splitting of the lowest subband. A spin splitting of 1.5-2.5 meV as $B\ensuremath{\rightarrow}0$ is deduced from the data. For magnetic fields applied at an angle $\ensuremath{\theta}$ to the interface, the beat positions scale as $cos\ensuremath{\theta}$ for small angles but increase steeply after a critical angle.

Evidence for spin splitting in In x Ga 1-x As/In 0.52 Al 0.48 As heterostructures as B-->0

The spin splitting in zero magnetic field which was recently reported in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/${\mathrm{In}}_{0.52}$${\mathrm{Al}}_{0.48}$As heterostructures is analyzed with use of the inversion-asymmetry, or ${\mathit{k}}^{3}$, term and the interface spin orbit or Rashba term. Comparison with experimental data shows that Rashba term is the dominant spin-splitting mechanism in these samples. Zero-field spin splittings of 2.5--2.75 meV are deduced from the perpendicular-field data. Analysis of tilted-magnetic-field data gives g factors that lie between -2 and -3.

Zero-field spin splitting in a two-dimensional electron gas.

We describe a novel quantum technology for possible ultra-fast, ultra-dense and ultra-low-power supercomputing. The technology utilizes single electrons as binary logic devices in which the spin of the electron encodes the bit information. Both two-dimensional cellular automata and random wired logic can be realized by laying out on a wafer specific geometric patterns of quantum dots each hosting a single electron. Various types of logic gates, combinational circuits for arithmetic logic units, and sequential circuits for memory have been designed. The technology has many advantages such as (1) the absence of physical interconnects between devices (inter-device interaction is provided by quantum mechanical spin-spin coupling between single electrons in adjacent quantum dots), (2) ultra-fast switching times of approximately 1 picosecond for individual devices, (3) extremely high bit density approaching 10 terabits cm-2, (4) non-volatile memory, (5) robustness and possible room-temperature operation with very high noise margin and reliability, (6) a very low power delay product ( approximately 10-20 J) for switching between logic levels, and (7) a very small power dissipation of a few tens of nanowatts per switching event. In spite of the above advantages, the technology also has some serious drawbacks in that the fan-out of individual logic devices may be small, wiring crossover is very problematic and the devices themselves have no inherent gain so that isolation between input and output is virtually non-existent. These are problems that plague all similar quantum technologies although they are seldom recognized as such. We will discuss these problems, and where possible, offer plausible solutions. In spite of these drawbacks, however, there are still enough attractive features of this technology to merit serious research. In this paper, we will describe how the spin-polarized single-electron logic devices work, along with the associated circuits and architecture. Finally, we will propose a new fabrication technique for realizing these chips which we believe is much more compatible with the demands of the technology than conventional nanofabrication methods.

http://iopscience.iop.org/article/10.1088/0957-4484/5/2/007/pdf

Supercomputing with spin-polarized single electrons in a quantum coupled architecture

Sidegating in GaAs integrated circuits can be eliminated in molecular beam epitaxially grown structure with the incorporation of a GaAs buffer layer grown at low substrate temperatures (200–300 °C). We have grown two films which were identical except one had the low‐temperature buffer layer included in the film structure. The films were modulation‐doped heterojunctions designed to produce a high‐mobility two‐dimensional electron gas. The electrical characteristics of the two‐dimensional electron gas were identical for the two samples. No deleterious effect on the mobility or carrier density was observed with the incorporation of the low‐temperature buffer layer. At 4.2 K both films exhibited carrier densities of 4×1011 cm−2 and mobilities of (1.4–1.7)×106 cm2/V s in the dark. After a brief illumination at 4.2 K, the samples exhibited carrier densities of 5×1011 cm−2 and mobilities of (1.6–2.0)×106 cm2/V s. These electron mobilities are comparable to the highest electron mobilities ever obtained at these e...

Biswajit Das

Papers

Electronic analog of the electro‐optic modulator

Evidence for spin splitting in In x Ga 1-x As/In 0.52 Al 0.48 As heterostructures as B-->0

Zero-field spin splitting in a two-dimensional electron gas.

Supercomputing with spin-polarized single electrons in a quantum coupled architecture

Effect of a GaAs buffer layer grown at low substrate temperatures on a high‐electron‐mobility modulation‐doped two‐dimensional electron gas