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Number 413, February 4, 1999 by Phillip F. Schewe and Ben Stein
THE FIRST 3D PHOTONIC CRYSTAL operating at a wavelength of 1.5 microns, the all- important preferred wavelength for light traveling down optical fibers, has been devised by scientists at Sandia (Shawn Lin, slin@sandia.gov). Basically, a photonic crystal is to light what a semiconductor is to electrons: some photon energies are permitted while others are excluded. The exclusion comes about by a careful interleaving of materials with very different indices of refraction. The Sandia crystal is actually a tiny pile of criss-crossed polysilicon rods with air in between. Photonic crystals will be ingredients in future optical transistors---by deflecting light they will be able to act as optical switches at THz speeds; by trapping light they will be able to produce optical amplification within cavities. The crystals will also be part of other optical integrated circuit components such as low-power nanolasers and as waveguides. (Optics Letters, 1 Jan 1999; see also Physics Today, Jan 1999. Figure at Physics News Graphics.)
MAGNETOELECTRONICS, SPIN ELECTRONICS, AND SPINTRONICS are different names for the same thing: the use of electrons' spins (not just their electrical charge) in information circuits. One magnetoelectronic device is the magnetic hard drive based on the giant magnetoresistance (GMR) effect. In a GMR material, consisting of a stack of alternating layers of magnetic and nonmagnetic atoms, a small magnetic field can produce a large change in electrical resistance. Already a billion dollar business, GMR read heads will boost disk drive densities from 1 to 20 Gbits, and GMR might be incorporated into random access memory units as well (Gary Prinz, Science, 27 Nov 1998). The latest demonstration of spin versatility is the organized movement of a herd of spins over a lateral distance of 100 microns. In an experiment at UC Santa Barbara, David Awschalom first aligned the spins of a swarm of electrons and then nudged them across a semiconductor strip without the spin bunch falling apart. Such coherence will be necessary if spin currents are to transport information from place to place, particularly in quantum computers. (Nature, 14 Jan 1999.)
THE ROLE OF PHYSICS IN BIOLOGY is a venerable one. The lead article in the 14 January issue of Nature describes how the borrowing continues, chiefly through application of versatile sensors and data management in such areas as genetic sequencing. But more than technology transfer is at work, and several new multidisciplinary institutes are being built (Stanford, Berkeley, Princeton, and Chicago) to cross-fertilize physics and bio/medical research Nature, 7 Jan 1999). One of the leaders at Stanford, for example, is Steven Chu, who has used his pioneering mageto-optic traps methods to study the physics of DNA molecules. The biology/physics connection was one of the themes of last week's AAAS meeting in Anaheim, where Hans Frauenfelder of Los Alamos described his motto as "Ask not what physics can do for biology but what biology can do for physics." To illustrate his point he cited the use of research on "energy landscapes" (essentially energy-level diagrams depicting transitions among various possible folded geometries, or conformations, of proteins) in the study of physics systems as "spin glasses," in which magnetic atoms are dispersed in an alloy with their spins oriented at haphazard angles. The evolving relation of physics and biology is even being felt at the high school level, where some schools are reversing the traditional biology-chemistry-physics sequence of courses, the better to introduce certain concepts, such as energy and force, needed for understanding the new higher biology (New York Times, 24 Dec 1998).
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