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Feshbach resonance in s-wave scattering states a BCS Cooper pair condensation at B-field just above the resonance where the scattering length a <0. Just wondering if the condensation has been observed in an experiment in any group? I was looking at a notes written in 2005 which claimed that this observation was the holy grail, and I seem not to be able to find a paper claiming that particular observation in experiment..

Many thanks :)

Simon

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up vote 4 down vote accepted

“BCS Cooper pair condensation” is theoretical method that is used to explain superconductivity/superfluidity in fermion systems. If we treat “BCS Cooper pair condensation” as a physical phenomenon, then I do not know if there is a general agreement on what is this physical phenomenon. ie what is the definition of “BCS Cooper pair condensation” as a physical phenomenon? If we define “BCS Cooper pair condensation” phenomenon as the phenomenon of superconductivity/superfluidity in fermion system, then the “BCS Cooper pair condensation” phenomenon has been observed. But such a definition is not proper since there are superconductivity/superfluidity that has no “BCS Cooper pair condensation” (such as charge 4e condensation).

So, before answering if the “BCS Cooper pair condensation” phenomenon has been observed or not, we need to define what is “BCS Cooper pair condensation” phenomenon in terms of EXPERIMENTS. This is actually a very tricky thing to do.

It may be worth while to start a new question: What is the “BCS Cooper pair condensation” as a physical phenomenon in terms of EXPERIMENTS?

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Can we treat the Cooper pair as a boson? What is the difference between "BCS Cooper pair condensation" with Bose-Einstein condensation? –  Jeremy Mar 24 '13 at 17:14
    
"BCS Cooper pair condensation" further assumes that the pair is formed by two fermions. –  Xiao-Gang Wen Mar 24 '13 at 17:36

Yes! Here's an example from January 2004, for Cooper pair condensation with a < 0. DOI: 10.1103/PhysRevLett.92.040403

The authors conclude:

"The experimental realization of condensation in the BCS-BEC crossover regime demonstrated in this Letter follows more than two decades of theoretical investigation and initiates experimental study of this physics."

Here's a further paper from later that year that you might also be interested in, for repulsive (a > 0) Fermi condensates. DOI: 10.1103/PhysRevLett.92.120403

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