Re: Cooper pairs in superconductor



Sam Wormley wrote:
> p6 wrote:
> >
> > Has the so called cooper pairs in superconductor been
> > detected in actual experiments...
>
>
> PHYSICS NEWS UPDATE
> The American Institute of Physics Bulletin of Physics News
> Number 707 November 3, 2004 by Phillip F. Schewe, Ben Stein
>
> ACCELERATOR FOR BECs. Two research groups have banged quantum gases
> together at record high velocities. Both groups begin by cooling
> clouds of rubidium atoms to ultralow temperatures. Next, through
> magnetic manipulation the clouds could be split into two separate
> clouds, each containing a native population with a characteristic
> spin value. Physicists in the Netherlands (FOM Institute for Atomic
> and Molecular Physics and the University of Amsterdam) further cool
> the clouds to produce Bose-Einstein condensates (BEC) before using
> the same magnetic control over the atoms to urge the clouds back
> together again at an increasing speed. Earlier experiments had
> managed to "collide" separate BEC samples at slow speeds of mm/sec
> (slow in relation to the velocity of sound in the BEC---several
> mm/sec) in order to observe characteristic interference stripes, and
> affirm the intrinsic wavelike nature of BEC as a whole. Now, the
> Dutch experiment is able to achieve speeds of 20 cm/sec; in effect
> their apparatus is a linear accelerator for BECs. The respective
> clouds are about 10 microns in size; the relative size of the clouds
> and their initial separation (up to record distances of 4 mm) is
> analogous to the separation of two tennis balls on opposite sides of
> a tennis court. When the two "tennis balls" collide, a spherical
> interference pattern shows up (see animation at
> staff.science.uva.nl/~walraven/walraven/Highlights.htm).
> Why is the higher speed important? It's because below sound speed,
> the superfluid BEC behaves like one giant matter wave, while above
> sound speed the BEC behaves like a collection of individual atoms.
> So in this experiment it is more accurate to think of 100,000 atoms
> (in the one cloud) scattering with 100,000 atoms (in the other
> cloud) rather then to think of two interacting clouds. Furthermore,
> because the speeds are still slow, the atom-atom collision can still
> be thought of as being the collision of two waves (like separate
> ripples in a pond passing through each other). In other words, the
> experiment probes the interaction between atoms rather than between
> BECs. In the BEC accelerator, matter waves of atom pairs are
> scattered out of the clouds at an energy of 10^-7 eV. (Compare this
> to Fermilab's 10^12 eV energy scale.) These matter waves are a
> superposition of spherical-shaped "s" and dumbbell-shaped "d" waves
> and hence show quantum mechanical interference. This interference
> is being directly imaged for the first time (Buggle et al., Physical
> Review Letters, 22 October 2004; contact Jeremie Leonard,
> jleon...@xxxxxxxxxxxxxx), and yields accurate measurement of the
> interaction properties between ultracold atoms. Comparable
> observations are being reported by physicists from the University of
> Otago in New Zealand, although in
> this experiment the atoms were at microkelvin temperatures but did
> not constitute a BEC. (Thomas et al., Physical Review Letters, 22
> October 2004; contact Niels Kaergaard, n...@xxxxxxxxxxxxxxxxxxx)
>
> COOPER PAIRS UNPAIRED. In a low-temperature superconductor
> electrons don't travel singly but in weakly tethered pairs, Cooper
> pairs. In a new experiment at the Forschungszentrum Karlsruhe in
> Germany, physicists have been able to send the two partners from
> Cooper pairs down separate wires spaced more closely than the
> effective size of the Cooper pairs themselves (see figure at
> www.aip.org/png). The Cooper pairs (which have the property that if
> one electron's spin is up, then the spin of its partner must be
> down) start out in a piece of superconducting aluminum and proceed
> to a frontier where they can travel down either of two
> normally-conducting and magnetized iron wires. (In general, when
> Cooper pairs move from a superconducting into a normally-conducting
> material they can maintain their pair status for a bit into the new
> material---a distance referred to as the normal-metal coherence
> length---before breaking up.) By magnetizing the wires so as to
> filter out pairings of any electrons that don't have the
> characteristic Cooper opposite-spin-orientation, and by varying the
> distance between wires, and by measuring the resistance across the
> iron wires, the experimenters can learn specific things about the
> Cooper pairing mechanism (such as how large the pair is under
> various circumstances). This work is part of the larger study of
> spintronics---the exploitation of electron spin for performing
> high-control electronics---and entangled states---the quantum
> behavior in which two spatially separated objects have a correlated
> behavior. (Beckmann et al., Physical Review Letters, 5 November
> 2004; contact Detlef Beckmann, detlef.beckm...@xxxxxxxxxx,
> 49-7247-82-6413
>
> ***********
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http://www.aip.org/png/2004/227.htm

Sam. The article you gave mentioned about how the
cooper pairs can be splitted by making two wires
less than the size of the cooper pairs (as mentioned
above). How in the world can they make a pair
less than the spacing of the cooper pairs which is
almost two atom distance apart. How the heck can
you make a wire almost the size of 1 atom (or even
3 atom)???

Pls. share what instrument or laboratory setup they
actually used to create a wire 3-atom size in diameter.

Tnx.

P6

.

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