---------- Forwarded message ---------- Date: Wed, 27 Jun 2001 13:34:00 -0400 (EDT) From: AIP listserver <physnews@aip.org> To: physnews-mailing@aip.org Subject: update.545 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 545 June 27, 2001 by Phillip F. Schewe, Ben Stein, and James Riordon ALL-OPTICAL BEC. Physicists at Georgia Tech have created and stored a Bose-Einstein condensate (BEC) of rubidium atoms in a trap using only laser beams, without the cumbersome magnet coils employed in traditional magneto-optic traps (MOTs). BECs have been transferred into purely optical traps before but this is the first time such a trap has produced the condensation itself, in which thousands or millions of atoms fall into a coherent single quantum state. What are the advantages of an optical design and why are BEC scientists excited about this result? (1) In the Georgia Tech approach the BEC occurs within seconds rather than in tens or hundreds of seconds. (2) Expensive, voltage-regulated power supplies for the magnets are no longer needed. (3) Atoms (such as magnesium or strontium) or molecules with magnetic moments not suitable for conventional traps, can be studied. (4) The faster condensation lessens the need for high vacuum. (5) Without bulky magnets all around, it will be easier to move the condensate into other enclosures, such as into cavities where interactions between the BEC and single photons can be studied. (Barrett et al., Physical Review Letters, 2 July2001; contact Michael Chapman, 404-894-5223, michael.chapman@physics.gatech.edu. Additional note: Physical Review Letters will, as of its 2 July issue, move to a continuous online publication, according to which an article's publication date will coincide with the day on which it is posted online; its print date will be the cover date of the paper issue of PRL in which the article appears in printed form. Furthermore, the printed cover of each issue will carry an illustration from one of the articles therein. The first such figure is associated with this all-optical BEC story.) SEMICONDUCTING MAGNETS AT HIGH TEMPERATURE. For water the melting temperature is where crystal turns to liquid. For magnets the Curie temperature is the point above which the lined-up spins of a ferromagnet fall out of alignment and the material becomes nonmagnetic. Recently the calcium-boron compound CaB6, doped with lanthanum, was observed to retain a modest ferromagnetism at temperatures as high as 900 K, surprising for a compound not containing the traditional magnetic metals such as nickel or iron. Now physicists in The Netherlands (Paul Kelly, University of Twente, p.j.kelly@tn.utwente.nl, 31-53-489-3166) suggest that CaB6 is not a metal, as has been thought, but actually a semiconductor. One obstacle so far to the realization of spintronics, the kind of electronics in which electron spin and not just electron charge plays a part, has been the difficulty of mixing semiconductors and magnetic metals. Hence the value of a semiconductor that starts out as a magnet and remains magnetic well above room temperature. Spintronics analogues of typical semiconductor functions, such as rectification and amplification, would now be possible.. In addition to magnetic sensor and memory applications, entirely new possibilities such as reprogrammable logic might be brought within reach. (Tromp et al., Physical Review Letters, 2 July 2001) ULTRAVIOLET FROM LEDs AND FEL's. Light at almost any wavelength is a useful tool for exploring the material world, but as the wavelength shrinks more information can be encoded into a given light pulse and, when used in a microscope, the light will have greater resolving power. Here are two notable examples of attaining ultraviolet radiation. First, scientists at Argonne's Advanced Photon Source have achieved UV radiation at a wavelength of 385 nm in a free-electron-laser (FEL) setup. In an FEL a beam of high energy electrons is sent through a sequence of magnets which cause the electrons' trajectory to undulate in such a way as to make the electrons radiate light which in turn interacts with the electrons. The researchers hope to extend their method up into the x-ray region (Milton et al., Science, 15 June 2001). The second result, from physicists at the National Institute for Materials Science in Tsukuba, Japan is a report of UV emission (235 nm) from a light emitting diode (LED) made by putting a boron-doped diamond layer up against a phosphorus-doped diamond layer. (Koizumi et al., Science 8 June 2001 -- ____________________________________________________________________ Whereof one cannot speak, thereof one must be silent. Ludwig Wittgenstein The Armadillo Group ,::////;::-. James Choate Austin, Tx /:'///// ``::>/|/ ravage@ssz.com www.ssz.com .', |||| `/( e\ 512-451-7087 -====~~mm-'`-```-mm --'- --------------------------------------------------------------------