QUASI-PARTICLE INTERACTIONS IN 2-DIMENSIONAL AND 3-DIMENSIONAL SUPERCONDUCTORS

I investigate the difference between the quasiparticle properties in t wo-dimensional (2D) and three-dimensional (3D) s-wave superconductors. Using the original BCS model for the pairing interaction and direct C oulomb interaction I show that quasiparticle interactions lead to a st ronger energy dependence in the single-particle self-energies in 2D th an in 3D superconductors. This difference arises from the presence of the low-lying collective mode of the order parameter in the 2D case wh ich ensures that oscillator strength in the response function is at lo w frequencies, similar to Delta. This strong quantitative difference b etween 2D and 3D superconductors points to the importance of treating quasiparticle interactions in low-dimensional superconductors rather t han assuming that renormalizations remain unchanged from the normal st ate.