Science News: Topological insulators, first proposed in 2005, allow electrons flowing along their surfaces to pass obstacles with no difficulty. Now Mordechai Segev of the Technion–Israel Institute of Technology in Haifa and his colleagues have extended the realm of topological insulators to include photons. They etched hundreds of helical waveguides into a block of glass to serve as wires for light. Because the waveguides were packed into a tight honeycomb structure, the light in one waveguide would interfere with the light in another and they would cancel each other out, except along the outer edge of the waveguides. That resulted in photons being steered to the waveguides’ edges and confined to the surface of the glass. When they reached an edge of the glass block, the photons made the turn and continued on their way, and none were scattered by surface imperfections. Segev’s team believes the discovery can be adapted for optical transmission technology to increase data transfer capabilities.
Category Archives: Condensed matter
The search for Higgs-like behavior in solid-state systems
Nature: In 1981 two theorists proposed that the superconductor niobium selenide could manifest behavior analogous to the Higgs mechanism that bestows mass on subatomic particles. Both the effect in NbSe2 and the Higgs mechanism arise from vibrations in fields that synchronize the oscillations of other particles. Now that, 31 years later, direct evidence has been found for the Higgs particle, solid-state physicists are hoping to better understand their own Higgs-like effect. They have already found that not all superconductors show the effect and that the behavior is also present in some antiferromagnets and some Bose–Einstein condensates. The use of solid-state experiments to study Higgs-like behaviors provides researchers significantly cheaper and smaller setups than large colliders. And it won’t be the first time that solid-state physics has influenced particle physics. In formulating his version of the theory of his namesake particle, Peter Higgs made use of a symmetry-breaking mechanism that Philip Anderson had identified previously in superconductors.
Below absolute zero reached in quantum gas
Nature: Absolute zero corresponds to the theoretical state in which the average energy of a system of particles is zero. During the normal state of a gas, the majority of the particles are at energies near the average, with just a few at higher energy levels. Theorists predicted in the 1950s that if a gas could be created in which the situation was reversed—the majority of the particles had higher energy levels—then the temperature could drop to below absolute zero. Ulrich Schneider, with Ludwig-Maximilians University in Munich, and his colleagues appear to have done just that. Using lasers and magnetic fields, the researchers arranged a stable lattice structure out of a quantum gas of potassium atoms. Quickly adjusting the magnetic field caused the atoms to attract rather than repel each other, and they shifted from their lowest-energy state to a high-energy state. Normally, that would cause the lattice to collapse, but the researchers used the lasers to make it too difficult for the atoms to leave their positions. The result is a gas that has a temperature just a few billionths of a degree below absolute zero. The experiment opens the way to potential stable states of exotic materials, and the theoretical behavior of other systems at sub-absolute-zero temperatures may provide some answers about cosmological phenomena such as dark energy.
New material is one-sixth as heavy as air
Euronews: The record for the world’s lightest material has been claimed by a new material called aerographite. Fabricated by Matthias Mecklenburg of Hamburg University of Technology and his colleagues, aerographite consists of interwoven threads of carbon nanotubes, each about 15 nm in diameter. With a density of just 0.2 mg/cm2, the mesh-like material is so light that the slightest movement in the lab stirs up currents that can blow it away. Mecklenberg envisions using aerographite for applications, such as filtration and catalysis, for which both lightness and a large surface area are needed.
How to supercool polar molecules
Ars Technica: Do supercooled molecules exhibit interesting properties such as superfluidity or form Bose–Einstein condensates the way supercooled atoms do? To find out, Martin Zeppenfeld of the Max Planck Institute of Quantum Optics in Germany and his colleagues have developed a method to reduce molecules—which are more polarized than atoms—to temperatures near absolute zero (−273.15 °C). They sent a stream of fluoromethane (CH3F) molecules into a trap of standing microwaves crossed with an IR laser. The combination of excitation by the laser and the jostling from the radio waves caused the molecules to rapidly lose energy. By continually adjusting the frequency of the radio waves and repeating the process over and over—a technique called Sisyphean cooling—the researchers were able to lower the temperature of the molecules to near absolute zero for at least 27 seconds.
Powerful x-ray laser creates solid-density plasma
Science Daily: Researchers at the US Department of Energy’s SLAC accelerator laboratory used rapid-fire laser pulses to flash-heat a tiny piece of aluminum foil to about 2 million °C. The experiments used SLAC’s Linac Coherent Light Source, which is a billion times brighter than any other x-ray source, to both create and probe the sample. “Making extremely hot, dense matter is important scientifically if we are ultimately to understand the conditions that exist inside stars and at the center of giant planets within our own solar system and beyond, ” said Sam Vinko, a postdoctoral researcher at Oxford University and lead author of the group’s paper published in Nature.
Effectiveness of UK’s neutron source jeopardized by lack of funding
Guardian: Hundreds of scientific experiments are being dropped by British universities because of budget shortfalls at ISIS, one of the UK’s major research facilities, writes Ian Sample for the Guardian. Built in the early 1980s at a cost of some $625 million, ISIS is a pulsed neutron and muon source used to probe the structure and microscopic processes of condensed matter. But it currently operates at only two-thirds capacity because the UK government has balked at paying the approximately $4.5 million in electrical and other miscellaneous annual costs to keep it running. As a result, ISIS receives twice as many applications as it can accommodate, and many scientists have given up applying. “The damage to the research base in UK universities across a number of disciplines is out of all proportion to the cost saving,” said Jon Goff at the University of London. “The saving comes mainly from electricity costs, and it equates in financial value to a single research grant to one group in a university. For this we lose a third of the science. . . . This substantially affects the international competitiveness of UK research.”
Antihydrogen atoms trapped one at a time for 0.17 seconds
Nature: The ALPHA collaboration at CERN has succeeded in creating then trapping single atoms of antihydrogen. The collaboration reported their findings yesterday in Nature. ALPHA and another, rival team at CERN called ATHENA had created antihydrogen eight years ago, but neither team had trapped any antiatoms. The confinement time achieved by ALPHA, 0.17 s, is long enough to perform experiments, but the atoms are too warm to yield results that might reveal any theory-challenging differences between the behavior of matter and antimatter.
South Korean company places largest-ever order for superconducting cable
Nature: LS Cable, a South Korean company based in Anyang-si near Seoul, is taking part in a program to modernize South Korea’s electricity grid. As part of that effort, LS Cable has ordered 3000 km of high-Tc superconducting wire from the Devens, Massachusetts-based American Superconductor. Although the dollar value of the sale has not been announced, its scale makes it the largest for superconducting wire. Nature‘s Joseph Milton reports on the deal and its implications.
How science is being used to find glacier entombed aviators
New York Times: In December 1942, John Pritchard and two other Coast Guard aviators were listed as missing after their plane lost radio contact—and presumably crashed—during a storm off the southeast coast of Greenland.
Now, 68 years later, the Coast Guard has commissioned a private recovery team to try to locate, excavate and repatriate the three men entombed in a J2F-4 Grumman Duck biplane (see left image) buried in a glacier there. The team set out last month with an arsenal of top-of-the-line technology: ground-penetrating radar, which can detect metallic objects close to the surface; advanced ice-melting equipment, which can pinpoint buried objects as it dissolves the ice around them; a camera that can take pictures from inside deep hollows of ice; and sensors to track the speed the glacier is moving before the plane, and bodies move out to sea.