Experiments underway to validate topologically insulating stanene as first room temperature lossless conductor 

Constantly losing energy is something we deal with in everything we do. If you stop pedaling a bike, it gradually slows; if you let off the gas, your car also slows. As these vehicles move, they also generate heat from friction. Electronics encounter a similar effect as groups of electrons carry information from one point to another. As electrons move, they dissipate heat, reducing the distance a signal can travel. DARPA-sponsored researchers under the Mesodynamic Architectures (Meso) program, however, may have found a potential way around this fundamental problem.

Meso program researchers at Stanford University recently predicted stanene will support lossless conduction at room temperature. Stanene is the name given by the researchers to 2-D sheets of tin that are only 1-atom thick. In a paper appearing in Physical Review Letters the team predicts stanene would be the first topological insulator to demonstrate zero heat dissipation properties at room temperature, conducting charges around its edges without any loss. Experiments are underway to create the material in laboratory conditions. If successful, the team will use stanene to enhance devices they are building under the Meso program.

“We recently realized there is another state of electronic matter: a topological insulator. Materials in a topologically insulating state are like paying for the gasoline to accelerate your car to highway speeds, but then cruising as far as you want on that highway without using up any more gas,” said Jeffrey Rogers, DARPA program manager. “Experiments should tell us what penalty electrons would pay for connecting to stanene in a practical application. However, the physics of stanene point to zero dissipation of heat—meaning electrons take an entropy hit once and then travel unimpeded the rest of the distance.”    

Researchers at Stanford reported the first topological insulators in 2006 under a previous DARPA effort known as the Focus Center Research Program. The current Meso program developed the theory for stanene as part of research into more efficient ways to move information inside microchips. Other materials’ capabilities have come close, but only at temperatures that require extreme sub-zero temperatures created with bulky methods such as liquid helium.   

“Stanene is a bold, yet compelling prediction,” said Rogers. “If the experiments underway confirm the theory, the application of a new lossless conductor becomes a very exciting prospect in the world of electronics. A host of applications—almost any time information is moved electronically from one place to another—could benefit.”

Latest Release Enhances Design of Photonic Components and Optical Networks

Highlights:

    --  Enhanced modeling of optical surface scattering for subwavelength optical components
    --  Faster photonic device simulations
    --  Expanded Multi-Physics utility for analysis of physical effects on photonic devices
    --  Flexible modeling and simulation of Reconfigurable Optical Add Drop (ROADM) networks
    --  Compliance with latest Optical Transport Network (OTN) standards

Synopsys has announced the availability of version 2013.12 of the Synopsys RSoft products, its industry-leading family of software tools for photonic and optical network design. This latest release delivers new modeling and analysis features as well as simulation speed improvements in the RSoft Photonic Component Design Suite. In addition, the release delivers enhancements in the RSoft MetroWAND network design tool to streamline network modeling, design and service planning.

Enhanced Modeling of Optical Surface Scattering
Two products in the Photonic Component Design Suite, the DiffractMOD and FullWAVE simulation tools, can now generate a Bidirectional Scattering Distribution Function (BSDF) file that contains scattering information for periodic optical structures, such as subwavelength diffractive surface gratings. The BSDF can be applied to a finite optical beam that covers more than one period to determine reflection and transmission characteristics of a structure. This provides a flexible, highly accurate method for modeling an optical surface's scattering properties, and helps optical designers achieve stringent size, weight and cost targets more easily.

The RSoft BSDF files can be imported into Synopsys' LightTools illumination design software to facilitate the design of lighting systems with small-feature, diffractive optical structures such as nano-structured LEDs. The BSDF data can also be used in Synopsys' CODE V optical design software, in its Beam Synthesis Propagation tool. This enables efficient analysis of micro-optical components used in applications that incorporate both illumination and imaging elements, like digital projector systems.

"The BSDF enhancements in the RSoft Photonic Component Design Suite provide a powerful new way for designers to model nanotechnology applications," said George Bayz, vice president and general manager of the Optical Solutions Group at Synopsys. "The RSoft BSDF's compatibility with LightTools and CODE V extends the modeling capabilities to a wide range of illumination and imaging applications."

Simulation Speed and Performance Enhancements
The RSoft BeamPROP tool has enhanced multi-threading capabilities that dramatically improve simulation speed and new Perfectly Matched Layer (PML) boundary conditions that provide improved performance for complex radiation patterns. FullWAVE has optimized continuous wave (CW) dispersive simulations for improved simulation speed, as well as a new dispersion fitting utility to create dispersive material models to use in simulations for multi-wavelength systems.

Expanded Multi-Physics Utility
The RSoft Multi-Physics Utility accounts for the effects of electrodes, heaters, stress and carriers on the refractive index profile during photonic device simulation. The Carrier Effects feature in this utility has been expanded to include:


    --  The ability to use complex index perturbations
    --  Generation of the photonic device's frequency response
    --  The ability to import custom, user-defined doping profiles
    --  Many new analysis outputs, including carrier density, current vs.
        voltage (I-V), resistance vs. voltage (R-V), and capacitance vs. voltage
        (C-V) plots
ROADM Network Design
MetroWAND 2013.12 delivers a new design engine option that allows flexible modeling and simulation of ROADM networks. Key capabilities include:


    --  Design and optimization of capacity allocation, end-to-end fiber layer
        performance validation and automatic selection and placement of ROADM
        network elements from the equipment library of choice
    --  End-to-end grooming of traffic demands into wavelengths
    --  Automatic setting of optical attenuators to equalize power of all
        optical channels
    --  Placement of optimal dispersion compensation modules in ROADM nodes
    --  Addition of Wavelength Selective Switch (WSS) models to the equipment
        library
    --  Ability to display the internal architecture of a ROADM node
    --  Support for automatic- or manual-selection nodes to build ROADM modules
Compliance with Optical Transport Network Standards
MetroWAND has new features to support the latest ITU-T OTN design standards, including:


    --  Rate Definition Model to support ITU-T G.709 Optical Transport Units
        (OTU) and Optical Data Units (ODU)
    --  Flexibility to add custom client signals and mappings
    --  Vendor equipment library samples to support OTN signal rates

"MetroWAND provides us with a user friendly, highly accurate tool for designing optical networks that meet our performance metrics for non-linearity, polarization mode dispersion (PMD) and all other parameters of Dense Wave Division Multiplexing (DWDM) components," said R. Parameshwar, senior project manager of R&D at United Telecoms Limited (UTL). "For example, it has various routing algorithms like shortest path, minimum hop and minimum cost to determine various routing arrangements, customizable equipment library to suit UTL DWDM equipment, and it performs optical link engineering analysis by placing dispersion compensation modules and setting optical attenuators for power equalization."

Availability & Resources
Synopsys' RSoft products version 2013.12 are available now. Customers with a current maintenance agreement can download this version from the Synopsys website using their SolvNet® account.

One of the major hurdles in the development of faster electronic devices is the amount of heat produced by silicon microchips. This heat is created by the transport of electrical charges through transistors. Seiji Yunoki and colleague Shin-ichi Hikino from the RIKEN Center for Emergent Matter Science in Wako have now proposed a device that instead of moving electrons is able to transport information using electron spin over long distances1


Moving electrons through a material creates intense heat as the electrons bounce off the atoms in the device. Moving information by passing it from one electron to another without any electron movement would therefore eliminate this source of heat. The magnetic property of electrons—their spin—has been studied as a possible means of achieving such a scheme. However, conventional magnetic materials fail to provide the long-distance transport of information required for such a strategy. “It is well known that conventional spin current can propagate only short distances,” says Yunoki. “This is one of the most critical problems in the research of spintronics.”


The spintronics scheme proposed by Yunoki and Hikino is based on sandwiching two adjacent thin magnetic films between superconducting layers. In conventional superconductors, the electrons are bound together in pairs formed by antiparallel electron spins, called a spin-singlet Cooper pair. However, with a ferromagnetic layer nearby, the spin of the two electrons in such a Cooper pair will align itself in the same direction as the magnetic field. These spin-triplet Cooper pairs (STCs) can move from the superconductor into the ferromagnetic layer, where they are very stable and long-lived (Fig. 1). 


The researchers have mathematically shown that within the ferromagnetic layer, the STC is able to carry spin currents over extended distances of several tens to hundreds of nanometers, and possibly even more if the magnetic material can be made with high purity. The spin transport happens without any charge current, and there is no voltage drop across the devices, meaning that no heat would be generated. 


So far, devices showing spin currents have been very difficult to realize, and such currents in the STC have never been observed. However, the simplicity of the proposed scheme promises its realization and could open a new era, says Yunoki. “We expect that the proposed superconductor–ferromagnet multilayer device can provide a new platform to study the spin transport of Cooper pairs in this developing research field.”

Thread-like semiconductor structures called nanowires, so thin that they are effectively one-dimensional, show potential as lasers for applications in supercomputing, communications, and sensing. Scientists at the Technische Universitaet Muenchen (TUM) have demonstrated laser action in semiconductor nanowires that emit light at technologically useful wavelengths and operate at room temperature. They now have documented this breakthrough in the journal Nature Communications and, in Nano Letters, have disclosed further results showing enhanced optical and electronic performance.

"Nanowire lasers could represent the next step in the development of smaller, faster, more energy-efficient sources of light," says Prof. Jonathan Finley, director of TUM's Walter Schottky Institute. Potential applications include on-chip optical interconnects or even optical transistors to speed up supercomputers, integrated optoelectronics for fiber-optic communications, and laser arrays with steerable beams. "But nanowires are also a bit special," Finley adds, "in that they are very sensitive to their surroundings, have a large surface-to-volume ratio, and are small enough, for example, to poke into a biological cell." Thus nanowire lasers could also prove useful in environmental and biological sensing.

These experimental nanowire lasers emit light in the near-infrared, approaching the "sweet spot" for fiber-optic communications. They can be grown directly on silicon, presenting opportunities for integrated photonics and optoelectronics. And they operate at room temperature, a prerequisite for real-world applications.

Tailored in the lab, with an eye toward industry

Tiny as they are – a thousand times thinner than a human hair – the nanowire lasers demonstrated at TUM have a complex "core-shell" cross-section with a profile of differing semiconductor materials tailored virtually atom by atom.

The nanowires' tailored core-shell structure enables them to act both as lasers, generating coherent pulses of light, and as waveguides, similar to optical fibers. Like conventional communication lasers, these nanowires are made of so-called III-V semiconductors, materials with the right "bandgap" to emit light in the near-infrared. A unique advantage, Finley explains, is that the nanowire geometry is "more forgiving than bulk crystals or films, allowing you to combine materials that you normally can't combine." Because the nanowires arise from a base only tens to hundreds of nanometers in diameter, they can be grown directly on silicon chips in a way that alleviates restrictions due to crystal lattice mismatch – thus yielding high-quality material with the potential for high performance. 

Put these characteristics together, and it becomes possible to imagine a path from applied research to a variety of future applications. A number of significant challenges remain, however. For example, laser emission from the TUM nanowires was stimulated by light – as were the nanowire lasers reported almost simultaneously by a team at the Australian National University – yet practical applications are likely to require electrically injected devices.

Nanowire lasers: a technological frontier with bright prospects

The newly published results are largely due to a team of scientists who are beginning their careers, under the guidance of Dr. Gregor Koblmueller and other senior researchers, at the frontier of a new field. Doctoral candidates including Benedikt Mayer, Daniel Rudolph, Stefanie Morkötter and Julian Treu combined their efforts, working together on photonic design, material growth, and characterization using electron microscopy with atomic resolution.

Ongoing research is directed toward better understanding the physical phenomena at work in such devices as well as toward creating electrically injected nanowire lasers, optimizing their performance, and integrating them with platforms for silicon photonics.

"At present very few labs in the world have the capability to grow nanowire materials and devices with the precision required," says co-author Prof. Gerhard Abstreiter, founder of the Walter Schottky Institute and director of the TUM Institute for Advanced Study. "And yet," he explains, "our processes and designs are compatible with industrial production methods for computing and communications. Experience shows that today's hero experiment can become tomorrow's commercial technology, and often does."

SAN FRANCISCO, CA -- AMD (NYSE:AMD) today announced the new AMD Athlon(TM) XP processor, reportedly the world's highest-performance processor for desktop PCs. AMD also announced plans to drive an initiative to develop a reliable processor performance metric that PC users can trust. The True Performance Initiative reflects AMD's continued commitment to business and home PC users.

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