i think the application of the second story has been dubbed 'spintronics'.
there's a wikipedia entry on it.
http://en.wikipedia.org/wiki/Spintronics


----- Original Message ----- From: "Alan Sondheim" <[EMAIL PROTECTED]>
To: <WRYTING-L@LISTSERV.WVU.EDU>
Sent: Thursday, November 09, 2006 9:10 AM
Subject: Physics News Update 800


PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 800 November 9, 2006  by Phillip F. Schewe, Ben Stein,
and Davide Castelvecchi                       www.aip.org/pnu

COHERENT EXCITON MATTER has been reported by a UC San Diego group.
They say their cold swarm of excitons acts like a Bose-Einstein
condensate (BEC) but might also be some new kind of quantum
condensate in which many particles act as if they were a single
entity.  Excitons are artificial tiny paired objects adrift in a
semiconductor and consist of an electron excited from its home
orbital plus a vacancy left behind.  The negatively charged electron
and the positively charged hole are bound to each other and will
usually, after a nanosecond or so, recombine, an event which knocks
the electron back into its home band and releases a tiny parcel of
light.  This is how light emitting diodes (LEDs) produce their
illumination.  In the UCSD experiment, the excitons live much longer
than usual--long enough to study as if there were a species of
atom--since the pair partners are held somewhat apart in nano-size
structures (quantum wells) in the body of the semiconductor sample.
The excitons can move about in the plane of the quantum well
semiconductor structure and, in a 20-micron-wide ring, constitute a
sort of gas which can be cooled down to ultralow temperatures.  When
chilled below 5 K, this gas began to show signs that it had
spontaneously condensed into a kind of quantum coherent state.  Just
as atomic BECs (in which atoms are cooled to the point where their
matter waves overlap and become, in effect, a single coherent
quantum system) are imaged by releasing the atoms from their
confining magnetic fields, so in this case the exciton condensate
reveals itself by telltale photons.  The photons, coming from the
annihilation of electrons with their hole partners, leave the ring
area, enter an optical device and, in the form of waves (which are
proxies
for the original excitons), produce a high-contrast interference
pattern, suggesting the coherent nature of the exciton gas.
Furthermore, the contrast of the interference fringes provides the
coherence length--about 2 microns (images at
http://ucsdnews.ucsd.edu/graphics/images/2006/exciton06_bg.jpg ).
San  Diego researcher Leonid Butov ([EMAIL PROTECTED])
believes
that controversy has surrounded previous reports of exciton
condensates and believes the new results are particularly clear in
displaying an interference pattern and in demonstrating quantum
coherence.  Like others who study coherent matter, Butov predicts
that practical
quantum devices will follow from this line of research.  (Yang et
al., Physical Review Letters, 3 November 2006; UCSD press release at
http://ucsdnews.ucsd.edu/newsrel/science/exciton.asp)

MEASURING ABSOLUTE MAGNETIC MOMENTS.  As long ago as Lord Kelvin's
time, a century ago, scientists recognized that a change in magnetic
environment could alter a material's electrical resistance.  Back
then this was a 5 percent effect.  By the 1990's, however, if the
material consisted of a sandwich of alternating magnetic and
nonmagnetic films the effect could amount to as much as 60 percent.
This "giant magnetoresistance" is now the operative mechanism behind
much of hard-drive and tape data storage.  By forcing the tiny
induced electric currents to jump across insulating layers as it
passes from one magnetic layer after another, the change in
resistance can be as high as 400 percent.  This translates into data
storage densities as high as 300 billion bits per square inch.
Fabio da Silva of the University of Colorado at Denver and Health
Science Center ([EMAIL PROTECTED]) and his colleagues at the
National Institute of Standards and Technology (NIST) in Boulder,
Colorado now employ the magnetoresistance effect not to store data
but to study the very process by which the tiny domains in the
storage medium are magnetized in the first place.  Using anisotropic
magnetoresistance (AMR), in which the resistance of the sample
changes when the magnetic material is remagnetized in a direction
different from that of the flowing current, the researchers could
measure the fundamental magnetism of the tiny (4-micron) domain
itself.  They hope these results can serve as a reference for
calibrating conventional magnetometers, devices that measure
magnetic fields in objects ranging from consumer electronics devices
to geophysical specimens. These results are being reported next week
at the AVS (vacuum science) symposium in San Francisco. (Wednesday,
November 15, 2006, 8:40am; Abstract at
http://www.avssymposium.org/paper.asp?abstractID=199 )

***********
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