New Material for Spintronics
Future computers and consumer devices may be based on the manipulation of spins rather than charges and a new material brings this one step closer to reality thanks to the work by researchers in the Laboratory of Photoelectron Spectroscopy at Ecole Polytechnique Fédérale de Lausanne. 

Spin manipulation requires spin-up and spin-down states to be separated in energy. In traditional electronics, both negative (electrons) and positive (holes) charges must be able to conduct. Both requirements can be fulfilled in conventional semiconductors, but only in very pure samples and at temperatures too low for practical applications.

Materials containing heavy elements such as lead or bismuth are under scrutiny, because their large spin-orbit interaction naturally leads to a large separation of spin states, e.g. in topological insulators.

But, researchers show by photoelectron spectroscopy that in BiTeI not only opposite spin states are largely separated in energy, opening the door to room temperature applications, but also that electron or hole states can be made to conduct by choosing one of two possible surface terminations.  BiTeI consists of alternating layers of bismuth, tellurium, and iodine, and the electrons in this material experience a strong spin-orbit interaction, which causes a large separation of spin states.

While the choice is random in their cleaved single crystals, the termination could be precisely controlled in thin films. Nanopatterning of such thin films may ultimately be used to produce the analog of p-n junctions for spins, the researchers said.

Wirelessly Powered Cardiac Device
A team of engineers at Stanford has demonstrated the feasibility of a super-small, implantable cardiac device that gets its power not from batteries, but from radio waves transmitted from outside the body. The implanted device is contained in a cube just eight-tenths of a millimeter in radius—small enough to fit on the head of pin.

The researchers have demonstrated wireless power transfer to a millimeter-sized device implanted five centimeters inside the chest on the surface of the heart—a depth once thought out of reach for wireless power transmission. The paper’s senior author was Ada Poon, an assistant professor of electrical engineering at Stanford.

The engineers say the research is a major step toward a day when all implants are driven wirelessly. Beyond the heart, they believe such devices might include swallowable endoscopes—so-called “pillcams” that travel the digestive tract—permanent pacemakers and precision brain stimulators. The devices could potentially be used for virtually any medical applications for which device size and power matter.

Controlling Terahertz Light
Controlling the direction (polarization) and oscillation amplitude of light (electromagnetic waves) has enabled the creation of devices with a wide range of functions and with the frequency of electromagnetic waves employed in such devices continuing to increase, it won’t be long until 10¹¹ hertz wireless communication becomes possible.

One obstacle to device development has been the difficulty of controlling the amplitude or polarization of terahertz (10¹²) electromagnetic waves, the frequencies to be employed in the next generation of RF communication devices.

Professor Yoshinori Tokura (University of Tokyo’s Graduate School of Engineering and RIKEN Strongly Correlated Quantum Science Research Group Director), Associate Professor Noriaki Kida (Graduate School of Frontier Sciences), Project Researcher Sandor Bordács (Graduate School of Engineering Quantum-Phase Electronics Center), and their colleagues have demonstrated the massive rotation of polarized light through 90 degrees for each millimeter it propagates through a Ba₂CoGe₂O₇ crystal, employing electron spin, the property that underlies magnetism.

In addition, the researchers demonstrated that light intensity can be increased or decreased up to 100% by application of a magnetic field due to what is termed the magneto-chiral effect, and is completely unrelated to the conventional effect of magnetic fields on light. Both of these phenomena were observed in the terahertz range, this research provides a step toward the realization of technology for the control of polarization and amplitude of terahertz electromagnetic waves.

Nanoresonators May Improve Cell Phone Performance
Researchers at Purdue University have learned how to mass produce tiny mechanical devices that could help cell phone users avoid the nuisance of dropped calls and slow downloads by easing congestion over the airwaves to improve the performance of cell phones and other portable devices.

Since there is not enough radio spectrum to account for everybody’s handheld portable device, explained Jeffrey Rhoads, an associate professor of mechanical engineering at Purdue University, the overcrowding results in dropped calls, busy signals, degraded call quality and slower downloads. To counter the problem, industry is trying to build systems that operate with more sharply defined channels so that more of them can fit within the available bandwidth but to do that more precise filters for cell phones and other radio devices are needed, systems that reject noise and allow signals only near a given frequency to pass.

The Purdue team has created devices called nanoelectromechanical resonators, which contain a tiny beam of silicon that vibrates when voltage is applied and can be manufactured with a nearly 100 percent yield.

The researchers stressed they are not inventing a new technology but making them using a process that’s amenable to large-scale fabrication, which overcomes one of the biggest obstacles to the widespread commercial use of these devices.

In addition to their use as future cell phone filters, such nanoresonators also could be used for advanced chemical and biological sensors in medical and homeland-defense applications and possibly as components in computers and electronics.

The devices are created using silicon-on-insulator, or SOI, fabrication – the same method used by industry to manufacture other electronic devices. The resonators can be readily integrated into electronic circuits and systems because SOI is compatible with complementary metal–oxide–semiconductor technology, or CMOS, another mainstay of electronics manufacturing used to manufacture computer chips.

–Ann Steffora Mutschler

Tags: cell phone performance, Ecole Polytechnique Federale de Lausanne, medical electronics, nanoresonators, Purdue University, spintronics, Stanford University, terahertz light, University of Tokyo

This entry was posted on Tuesday, September 4th, 2012 at 9:59 am and is filed under News Stories. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.