---------- Forwarded message ----------
Date: Wed, 27 Jun 2001 13:34:00 -0400 (EDT)
From: AIP listserver <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
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,
[EMAIL PROTECTED] 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, [EMAIL PROTECTED], 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 /:'///// ``::>/|/ [EMAIL PROTECTED]
www.ssz.com .', |||| `/( e\ 512-451-7087
-====~~mm-'`-```-mm --'-
--------------------------------------------------------------------
