T-rays will 'speed up' computer memory by a factor of 1,000

http://www.nanowerk.com/nanotechnology-news/newsid=44801.php

(Nanowerk News) Together with their colleagues from Germany and the Netherlands, scientists at the Moscow Institute of Physics and Technology (MIPT) have found a way to significantly improve computer performance. In their paper published in Nature Photonics ("Nonlinear spin control by terahertz-driven anisotropy fields"), they propose the use of the so-called T-waves, or terahertz radiation as a means of resetting computer memory cells. This process is several thousand times faster than the magnetic-field-induced switching.“We have demonstrated an entirely new way of controlling magnetization, which relies on short electromagnetic pulses at terahertz frequencies. This is an important step towards terahertz electronics. As far as we know, our study is the first to make use of this mechanism to trigger the oscillations of magnetic subsystems,” says Anatoly Zvezdin of Prokhorov General Physics Institute and MIPT, a coauthor of the paper and a USSR State Prize-winning scientist heading MIPT’s Laboratory of physics of magnetic heterostructures and spintronics for energy-saving information technologies.

The figure shows thulium orthoferrite (TmFeO2) spin and lattice structure on the left and the T-ray-induced transitions between the energy levels of thulium ions (Tm3+), which trigger coherent spin dynamics (memory switching), on the right. (click on image to enlarge)The rapidly increasing amounts of digital data that have to be manipulated, along with the growing complexity of the computation tasks at hand, compel hardware designers to achieve ever higher computational speeds. Many experts believe that classical computation is currently approaching a limit, beyond which no further increase in data processing speed would be practicable. This motivates scientists all over the world to investigate possibilities of entirely different computer technologies. One of the weak spots in modern computers retarding their evolution is memory: it takes time to complete every set/reset operation for a magnetic memory cell, and reducing the duration of this cycle is a very challenging task.A group of scientists that includes Sebastian Baierl of the University of Regensburg, Anatoly Zvezdin, and Alexey Kimel of Radboud University Nijmegen (the Netherlands) and Moscow Technological University (MIREA) proposed that electromagnetic pulses at terahertz frequencies (with wavelengths of about 0.1 millimeter, i.e., between those of microwaves and infrared light) could be used in memory switching instead of external magnetic fields. A more familiar device that makes use of the terahertz radiation is the airport body scanner. T-rays can expose weapons or explosives concealed under a person’s clothing, without causing any harm to live tissues.To find out, whether T-rays could be used for convenient memory states switching (storing “magnetic bits” of information), the researchers performed an experiment with thulium orthoferrite (TmFeO2). As a weak ferromagnet, it generates a magnetic field by virtue of the ordered alignment of the magnetic moments, or spins of atoms in the microcrystals (magnetic domains). In order to induce a reorientation of spins, an external magnetic field is necessary.However, the experiment has shown that it is also possible to control magnetization directly by using terahertz radiation, which excites electronic transitions in thulium ions and alters the magnetic properties of both iron and thulium ions. Furthermore, the effect of T-rays proved to be almost ten times greater than that of the external magnetic field. In other words, the researchers have devised a fast and highly efficient remagnetization technique—a solid foundation for developing ultrafast memory.The scientists expect their “T-ray switching” to work with other materials as well. Thulium orthoferrite, which was used in the experiment, happens to be convenient for the purposes of demonstration, but the proposed magnetization control scheme itself is applicable to many other magnetic materials.“There was a Soviet research group that used orthoferrites in their studies, so this was always kind of a priority field for us. Our research can be seen as a follow-up on their studies,” points out Anatoly Zvezdin.

Read more: T-rays will 'speed up' computer memory by a factor of 1,000 

3-D Mapping of Electrons Moving on a Material's Surface

By Alexander Hellemans

Scanned images of a semiconductor nanowire before the impact of an infrared pump pulse, then 50 femtoseconds after the pulse, when the movement of free electrons on its surface is visible, and 150 femtoseconds later, when the effect of the pump pulse has died out.

http://spectrum.ieee.org/nanoclast/semiconductors/nanotechnology/3d-mapping-of-electrons-moving-on-a-materials-surface?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+IeeeSpectrum+(IEEE+Spectrum)

Terahertz spectroscopy uses infrared light to probe matter and is widely used to investigate the electrical properties and behavior of semiconductor materials. By sending very short laser pulses, called probe pulses, in quick succession, it is possible to follow how these properties change over time when the material responds to a light pulse, for example. However, unlike x-rays, terahertz waves have relatively long wavelengths ranging from 3 to 3000 micrometers. And just as with optical microscopes, structures smaller than the pulses’ wavelength remain invisible.

Now researchers at the University of Regensburg in Germany have demonstrated that it is possible to dramatically increase the spatial resolution of terahertz spectroscopy by focusing the probe pulses on the needle of an atomic force microscope (AFM). They published this research in Nature Photonics yesterday.

AFMs are widely used tools in solid-state research. Scanning with the sharp tip of the AFM at a slight distance from the surface of a material and measuring the variation of the force between the tip and the material—which can be an electrostatic or van der Waals force, for example—allows the creation of an image of the surface in which individual atoms are visible.

But the Regensburg researchers took a different tack. Instead of measuring the force between the tip and the surface of the material, they measured the intensity of light scattered by the tip with a series of probe pulses. According to Rupert Huber, the physicist who led the research, this method, “Is a little like a conventional radio antenna, just downscaled to wavelengths of infrared radiation.”

The light pulse, which is an oscillating electromagnetic field, shifts electrons up and down along the shaft of the metallic tip.  However, because the electrons cannot travel beyond the tip, they accumulate at the very tip apex during each half cycle of the oscillating electromagnetic field. Since electrons are charged, they give rise to an intense burst light at the tip a very small area, called the near field, with roughly the size of the tip apex, explains Huber.

This setup, which the Regensburg team is calling a scattering-type near-field scanning optical microscope, or s-NSOM, confines light to an area that is only 10 nanometers across. Without the needle, one would be limited to about half the wavelength of the light, the diffraction limit that curtails the resolution of every conventional microscope. "In contrast, the near-field occupies a volume that is approximately nine orders of magnitude smaller than the usual diffraction limit,” Huber told IEEE Spectrum.

For their experiment, the Regensburg team used indium arsenide nanowires prepared by a group—who are coauthors of the Nature Photonics paper—at the Pisa site of CNRNano, a nanoscience institute of the Italian Research Council. Indium arsenide is a semiconducting material holding a promise for terahertz sources and infrared lasers.

They first hit the nanotube with a terahertz pump pulse, which caused the liberation of charge carriers in the nanowire. This allowed them to detect the presence of electrons moving at the surface of nanowire—a little like what you would see if you disturb an ants' nest. Immediately after the pump pulse, they sent a series of terahertz probe pulses lasting few femtoseconds each. The pulses produced the 10-nm flashes of confined light on the tip. The intensity of these flashes depends on how many electrons are roaming around on the surface of the nanowire. These electrons don't stay around long, however; so, for every new probe pulse, the intensity of scattered light by the tip decreases.

By moving the tip to a new location for each pump cycle, the researchers created a complete "film" of how the nanowire reacts to the pump pulse. Among the phenomena they documented was that the free electrons first disappeared at the ends of the nanowires.

There is no reliable alternative, as of now, for measuring local carrier densities on the few-femtosecond time scale with 10-nm resolution, says Huber. "It is extremely important to understand how carriers behave locally. This insight is crucial for future high-speed integrated electronics and lasers based on semiconductor nanowires," he adds.

Terahertz work wins student paper competition at CLEO

http://www.electrooptics.com/news/news_story.php?news_id=2185

Fabian Langer of University of Regensburg, Germany has won the annual Maiman Outstanding Student Paper Competition at CLEO 2014.

Langer won for his paper ‘CEP control of dynamical Bloch oscillations in a bulk semiconductor via ultra-intense multi-THz fields’. The grand prize of $3,000 and two honourable mentions were presented during the plenary talks and awards ceremony on 10 June at CLEO: 2014.

There were 965 submissions reviewed and scored by the CLEO 2014 technical programme committee, which selected 28 semi-finalists. Six finalists were chosen, who presented their research in a private session at the show. The presentations were judged based on innovation, research excellence and presentation ability.

Honourable mentions went to: Matthias Lauermann at the Karlsruhe Institute of Technology, Germany, for the paper ‘16QAM silicon-organic hybrid (SOH) modulator operating with 0.6 Vpp and 19 fJ/bit at 112 Gbit/s’, and Kevin O’Brien at the University of California, Berkeley, US, for the paper ‘Phase mismatch – free nonlinear propagation in optical zero-index materials’.

The Maiman Outstanding Student Paper Competition honours American physicist Theodore Maiman for his invention of the first working laser, and his other outstanding contributions to optics and photonics. It recognises student innovation and research excellence in the areas of laser technology and electro-optics. The award is endowed by a grant from HRL Laboratories, the IEEE Photonics Society and the APS Division of Laser Science and is administered by the OSA Foundation.

Additionally, 10 students received travel grants to attend CLEO 2014 as recipients of the Incubic/Milton Chang Student Travel Grants.

Related internet links

CLEO 2014
OSA Foundation
Maiman Outstanding Student Paper Competition