Re: Upended quantum physics in the news


"David Ewan Kahana" <dek@xxxxxxx> wrote in message
news:1140214310.162540.199870@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Glenn wrote:
<carlip-nospam@xxxxxxxxxxxxxxxxxxx> wrote in message
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Glenn <glennsheldon@xxxxxxxxxxxxx> wrote:


http://www.sciencedaily.com/upi/index.php?feed=Science&article=UPI-1-20060215-17171200-bc-us-spintheory.xml

PROVIDENCE, R.I., Feb. 15 (UPI) -- Rhode Island and Alabama
scientists
report creating, for the first time, a "spin triplet"
supercurrent
through a ferromagnet over a long distance.

Achieved with a magnet developed at Brown University and the
University of Alabama, the feat upends longstanding theories
of
quantum physics. [...]

What a terrible news article. I've read the paper in Nature,
and it
has nothing whatsoever to do with "upended quantum physics." It
shows
that a particular phenomenon which has been difficult to
demonstrate
-- superconductivity in a ferromagnet -- can be achieved with a
clever
enough choice of materials. This says nothing about the
fundamentals
of quantum physics; the theories of superconductivity and
ferromagnetism
involve quantum physics, but so does everything else in solid
state/
condensed matter physics. In fact, as the actual paper in
Nature
says,
the coexistence of superconductivity and ferromagnetism had
already
been observed (in iron under pressure), and behavior much like
what
the paper reported had been predicted from theory several years
before.

Here's the editor's summary of the article, which appeared in
Nature
439,
825-827 (16 February 2006):

Under most conditions, conventional superconductivity and
ferromagnetism are mutually exclusive. Although they have
been observed together in iron under pressure, the principle
holds as a rule. But now Keizer et al. describe a system in
which superconductivity and magnetism are finally seen
working
together. The material in which this occurs is chromium
dioxide,
well known as the active component of magnetic recording
tape.
It's a half-metallic ferromagnet, and can sustain a
Josephson
(or 'spin triplet') supercurrent that switches with the
direction
of magnetization.


[snip]

Here's something I just pulled out of my hat, off the internet:

http://www.cmp.liv.ac.uk/research_magnetism.php
"Theory predicts either an antiferromagnetic structure in the Mn
with
moments in the same direction as the ferromagnetic Fe, or a
helical
structure. The data show that this simple picture is wrong and
that
the moments in the Mn are perpendicular to those of Fe, see Fig.
4."

"Attempts to explain the mechanism of high-temperature
superconductors
have shown our understanding of the underlying quantum theory to
be
inadequate."

Why don't you try reading for comprehension instead of reading
for the purposes of obfuscation?

The clear meaning of the statement is that `our understanding
of the underlying quantum theory' of *high-temperature
superconductors* is inadequate.

Such a statement about the inadequacy of our understanding
can be applied to almost any quantum mechanical many body problem.
It's completely generic and just about content free.

Your understanding of theory is completely generic and just about
content free? Why are you responding.

This doesn't imply that our understanding of quantum theory is
inadequate or that quantum mechanics has been `upended.'

The article you posted is very badly written, for all the reasons
Steve Carlip and others have pointed out.

David



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