Pairing gap equation weak coupling

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SUMMARY

The discussion centers on the BCS pairing gap equation in the context of weak coupling, specifically when G\overline{ρ}<<1. It establishes that the pairing gap Δ is proportional to exp(-1/G\overline{ρ}), indicating that this relationship cannot be expressed as a power series in the interaction strength G. The conversation confirms the existence of a phase transition between superfluid and normal fluid states, characterized by the order parameter of cooper pair density, which breaks the electromagnetic U(1) symmetry in superconductors. This mechanism is applicable to various systems, with the specific symmetry breaking and particle types varying accordingly.

PREREQUISITES
  • Understanding of BCS theory and superconductivity
  • Familiarity with phase transitions in quantum systems
  • Knowledge of order parameters in condensed matter physics
  • Basic grasp of U(1) symmetry and its implications
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  • Research the implications of the BCS pairing gap equation in different physical systems
  • Study the role of cooper pairs in superconductivity
  • Explore phase transitions in quantum fluids and their characteristics
  • Investigate the significance of U(1) symmetry breaking in various condensed matter contexts
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Physicists, particularly those specializing in condensed matter physics, superconductivity researchers, and students studying quantum mechanics and phase transitions.

Maliphus
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In the limit of weak coupling, [itex]G\overline{ρ}<<1[/itex], the BCS pairing gap equation gives that [itex]Δ \propto exp(-1/G\overline{ρ})[/itex]. [itex]\overline{ρ}[/itex] is the level density.This cannot be developed as a power series in the interaction strength G. Does this imply that there is a phase transition between a superfluid and a normal fluid state? If so, how exactly?
 
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Yes, there is a phase transition. The order parameter is the cooper pair density and the phase transition breaks electromagnetic U(1) symmetry (in the case of superconductors). The mechanism has been transferred to other systems, so the symmetry broken, and the particles forming the condensate will depend on the system.
 

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