1/F Noise In The Superconducting State Of Quasi-Two-Dimensional Organic Conductors (Bedt-Ttf)(2)X-A Comparative Study

We report on resistance noise spectroscopy measurements in the superconducting state of two quasi-two-dimensional organic superconductors The superconducting state of beta -(ET)(2)SF5CH2CF2SO3 is homogeneous whereas kappa-(ET)(2)Cu[N(CN)(2)]Cl under pressure is located in the inhomogeneous region of the phase diagram, where antiferromanetic/insulating and superconducting phases coexist For the latter material the finite noise level even well below T-c is understood in the framework of a random resistor network. Furthermore the noise provides evidence for percolation-type superconductivity For homogeneous beta -(ET)(2)SF5CH2CF2SO3 however no indications of percolation effects are found the noise in the superconducting state vanishes and the normalized noise level S-R/R-2 is generally one order of magnitude lower (C) 2009 Elsevier B V All rights reserved