Coherent scattering in BCS semicon?

[2Tesla]

Hello experts,

I've had some fun reading the posts in the various forums, and now it's time for me to ask a question.

Is it possible to scatter light off of a BCS semiconductor such that the light can be considered to scatter from the coherent state of many Cooper pairs, rather than just one pair or one electron? I would think this would be an interesting phenomenon, as the kinematics of the scattering would involve the large collective momentum and energy of many electrons.

Thank you for your time.

 

[ZapperZ]

What is a "BCS semiconductor"?

Not that in a superconductor, optical spectroscopy measurements are typically done by collecting the reflected light. Comparing this to the original incoming light and using Kramers-Kronig transformation, one can obtain the transmitted component. This component can give you information on the supercurrent density, etc.

Zz.

 

[2Tesla]

Oops, what a horrible typo... My apologies. I meant superconductor, obviously.

So, just to clarify--any individual collision would be between one photon and *all* of the supercurrent? I ask because, in that case, it seems the collective momentum of all particles in the supercurrent (2*N*me*vdrift, where N is the large number of Cooper pairs and me is the electron mass) might overwhelm the momentum of a low-energy (say, red visible) photon and cause a large deflection. And then it would seem that you can choose the direction of the reflected light by changing the direction of the supercurrent.

(Assuming, of course, that the photon can penetrate to the supercurrent and surface states don't cause a problem.)

 

[ZapperZ]

One never does a "single photon scatters of a cooper pair". I've never seen such an experiment.

What has been done is the scattering of a lot of photons with a lot of cooper pairs (and other "normal electrons") in a superconductor. That experiment has been done.

Zz.

 

[2Tesla]

Ah, I think there is some confusion. I'm not talking about scattering off a single Cooper pair, but off of the coherent state of *all* of the Cooper pairs in the supercurrent.

Once the Cooper pairs have condensed into the ground state, they form a single coherent state, similar to a BEC. And in a BEC, as I understand it (and I may be wrong), one can scatter light from this entire state.

The reason I find this interesting, is that the momentum of this one coherent state, when in a supercurrent, must be large or comparable to that of a visible photon, since it has the mass of many many electrons.

Or am I so far off base that I'm completely incomprehensible to everyone reading?

 

[ZapperZ]

But isn't this what I've said. You essentially scatter off all the carriers, but you can look for signatures of scattering off those that are involved in superconductivity.

There are many papers that do this, and are able to extract the superfluid density. You may want to look, for example, at this paper:

http://arxiv.org/abs/cond-mat/0410719

Zz.