What's with 'virtual' phonons in BCS pairing?

In summary, virtual phonons are necessary to explain BCS pairing in type I superconductors. They originate from the lattice vibrations, but are actually the 'virtual' form of the phonons that describe e.g. static lattice deformations.
  • #1
Creator
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Can someone explain why virtual phonons are necessary to explain BCS pairing in type I superconductors. I thought phonons originated with the lattice vibrations. I read that it s the 'virtual" phonons that explains the pairing; how so? what am I missing ?
 
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  • #2
Real phonons are lattice deformations which can propagate freely, i.e. sound waves.
Virtual phonons are needed to describe e.g. static lattice deformations surrounding a perturbation, e.g. an electron. In the most simple limit this gives the rubber surface description of Cooper pairing: An electron behaves like a ball on a rubber surface, it creates a deformation of the surface and a second electron (ball) will fall into that hole.
 
  • #3
Creator said:
Can someone explain why virtual phonons are necessary to explain BCS pairing in type I superconductors. I thought phonons originated with the lattice vibrations. I read that it s the 'virtual" phonons that explains the pairing; how so? what am I missing ?

You are missing Quantum Field Theory.

The idea here is that one is trying to describe the interaction between two objects. Naively, in QFT, this is accomplished via the exchange of a virtual bosonic "particle". In E&M, it is the exchange of virtual photon. In condensed matter physics, it can be any boson that is the equivalent of a 'vacuum excitation'. In the case of conventional superconductivity, this is the virtual phonons.

In other cases, you can have an exchange of magnons, polarons, etc...

Zz.
 
  • #4
Thank you both for the replies. So the pairing is a result mostly of the virtual phonon exchange, and not the real phonons that originate in the lattice...or both? Can either of you describe the effect of each if possible.
2. So is it the virtual momentum exchange that causes the attractive potential,?
Thanks.
 
  • #5
if quantum tunneling is involved its all virtual
 
  • #6
kimcosmos said:
if quantum tunneling is involved its all virtual

No it doesn't. Show me the physics that says this.

This is also a necropost.

Zz.
 

FAQ: What's with 'virtual' phonons in BCS pairing?

1. What are virtual phonons in BCS pairing?

Virtual phonons are a mathematical construct used to explain the mechanism of superconductivity in the BCS theory. They are not physical particles but rather a way to describe the exchange of energy and momentum between electrons in a superconductor.

2. How do virtual phonons contribute to BCS pairing?

In the BCS theory, electrons are thought to form Cooper pairs due to the exchange of virtual phonons. This interaction reduces the repulsive Coulomb force between electrons, allowing them to overcome their natural repulsion and form a bound state.

3. Are virtual phonons necessary for BCS pairing?

The BCS theory does not require the presence of virtual phonons to explain superconductivity. However, they are a useful concept in understanding the mechanism of Cooper pair formation and have been experimentally observed in some cases.

4. How are virtual phonons related to lattice vibrations?

Virtual phonons are related to lattice vibrations, also known as phonons, through the concept of electron-phonon coupling. In a superconductor, the exchange of virtual phonons between electrons is thought to be mediated by the lattice vibrations.

5. Can virtual phonons explain all aspects of superconductivity?

No, virtual phonons alone cannot explain all aspects of superconductivity. While they play a crucial role in the BCS theory, other factors such as electron-electron interactions and the presence of impurities also contribute to the phenomenon of superconductivity.

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