Raman and microwave surface impedance measurements in the organic superconductor κ-Et 2Cu[N(CN) 2]Br xCl 1−x

Abstract

We report a Raman study of CH 2 and C=C vibrations for single crystals of the organic superconductor κ-Et 2Cu[N(CN) 2]Br xCl 1−x (nominal value x=.5) in both the normal and superconducting states (T c=l 1.3 K). The average charge transfer ρ=0.5 is estimated from the frequency of the C=C ring stretching Raman mode ν 3 (Ag). Raman results are discussed in connection with our previous study of the normal and superconducting states of Et 2Cu[N(CN) 2]Br. High sensitivity microwave surface impedance is also studied. The microwave resistance R s and microwave reactance X s are reported as a function of temperature in order to complement our Raman experiments and to determine precisely the critical temperature T c and the type of superconductivity.