Microwave conductivity in the pure and iodine-doped organic conductor α-(BEDT-TTF)2I3

Abstract

The microwave conductivity in dependence of temperature was measured on pure and iodine doped crystals of α-(BEDT-TTF)2I3 along the stack direction [100] and perpendicular to it [010]. The exposure times to iodine were varied in many steps between 2 min and 360 min. The contactless microwave technique enables to keep tbe same crystal in each case throughout all measurements. The results show that the microwave conductivity vs. temperature is not influenced distinctly by iodine doping. Only at the onset or the plateau range immediately below the metal-insolator transition at 135 K a small enhancement of the conductivity is found for exposure times larger than 60 min. In no case a transition to a supercooducting state is observed. Therefore recently reported superconductivity may be due to surface effects.