New materials to herd photons
Used in communication systems, optical networks employ isolators to keep light from reflecting backwards. Isolators also absorb photons, thereby reducing a signal in a system.

All of that may be unnecessary in the future, however. MIT, Zhejiang University in China, and the University of Texas at Austin have devised a new “metamaterial” that keeps photons moving in only one direction. This, in turn, could pave the way toward chips that move data with light.

Electromagnetic materials that lack so-called local time-reversal symmetry could enable these types of chips. Gyrotropic materials, for one, are the most promising.

Using such materials, researchers have devised a “metamaterial.” They also have made use of antennas of alternating orientations, which are connected by amplifier circuits. The antennas are embedded in a pair of circuit boards. The direction of current flow through the circuits determines the direction of the electromagnetic waves.

Electron interactions spotted in graphene
Graphene, a promising material for future transistors, consists of one-atom-thick planar sheets that are packed in honeycomb crystal lattice structures. But graphene is complex and doesn’t have a band gap, meaning it can’t be turned off in a system.

Researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the University of California at Berkeley are claiming a new breakthrough in this arena— they have demonstrated the electron interactions in graphene.

Using a scanning tunneling microscope (STM), researchers observed gated devices consisting of a graphene layer deposited atop boron nitride flakes. The flakes were placed on a silicon dioxide substrate.

Researchers observed how electrons and holes respond to a charged impurity placed on a gated graphene device. The charged impurities were cobalt trimers constructed on graphene.

“Theorists have predicted that compared with other materials, electrons in graphene are pulled into a positively-charged impurity either too weakly, the subcritical regime; or too strongly, the supercritical regime,” said Michael Crommie, a physicist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Physics Department.

“In our study, we verified the predictions for the subcritical regime and found the value for the dielectric to be small enough to indicate that electron–electron interactions contribute significantly to graphene properties. This information is fundamental to our understanding of how electrons move through graphene,” he added.

SWAN dives into study of molecules
Researchers from Iowa State University and Ames Laboratory have developed a new microscope technology that enables the study of single biological molecules.

Called standing wave axial nanometry (SWAN), the technology combines atomic force and optical microscope technologies. SWAN is able to image the axial location of a single nanoscale fluorescent object down to 3.7nm.

A standing wave, generated by positioning an atomic force microscope tip over a focused laser beam, is used to excite the fluorescence of an object. The axial position is determined from the phase of the emission intensity.

Researchers used SWAN to measure the orientation of single DNA molecules of different lengths. The technology can be used in the medical and other fields.

—Mark LaPedus

Tags: Ames Laboratory, electromagnetism, Iowa State University, Lawrence Berkeley National Laboratory, MIT, optical networks, standing wave axial manometry, SWAN, U.S. Department of Energy, UC Berkeley, University of Texas, Zhejiang University

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