Electrodynamics of molecular organic superconductors studied by $\mu $SR

The response of the superconducting charge carriers to an applied magnetic field has been probed in a number of organic superconductors using μSR. Systematic studies have been made of the in-plane superconducting penetration depth $\lambda $in superconductors based on the ET and BETS molecules. These studies have revealed a strong correlation between $\lambda $and Tc. This type of correlation was first noted in high Tccuprates by Uemura et alwho found a linear relation between Tcand $\lambda ^{-2}$. In the case of organic superconductors, however, we find that the overall correlation is better described as T$_{c}\propto \lambda ^{-3}$. Understanding this characteristic trend should provide some important clues about the nature of the superconductivity in the organic superconductors; several possible models are considered here for describing this behaviour. It is concluded that models in which the superconducting carrier concentration is tied to the nominal band filling are inconsistent with the observed scaling behaviour. Key words.London penetration depth – Superconducting transition temperature.