Relation between transition temperature, London penetration depth and Kosterlitz-Thouless behavior in superconductors

We sketch the theory of London superconductors with a complex order parameter undergoing a phase transition dominated by thermal fluctuations. Thus, the theory is essentially that of superfluid helium, appropriately modified. We derive relations between the transition temperature Tc, the London penetration depth, the phase correlation length, the fall of Tc with reduced thickness in thin slabs and the corresponding appearance of Kosterlitz-Thouless behavior. Our analysis of recent electronic-specific heat, μSR measurements and experiments on ultrathin slabs reveal that this scenario applies to a large class of superconductors that includes the cuprates, bismuthates and fullerenes. (orig.)