Non-linear transport in /spl alpha/-(BEDT-TTF)/sub 2/I/sub 3/

Summary form only given. The two-dimensional organic conductor /spl alpha/-(BEDT-TTF)/sub 2/I/sub 3/ undergoes a metal-insulator phase transition of unknown origin at T/sub MI/ = 135 K. We studied the electrodynamic response of /spl alpha/-(BEDT-TTF)/sub 2/I/sub 3/ in a extremely wide range of frequency, covering microwave and millimetel wave frequencies as well as the optical spectral range, and find a frequency dependent conductivity up to 1000 cm/sup -1/ in the low temperature phase. This is accompanied be a non-linear transport with a smooth onset at about 10 V/cm. Our X-ray studies show no indication of superstructure reflections and clearly rule out the formation of a charge density wave ground state. The lack of a temperature dependence in the millimeter wave conductivity between 20 K and 100 K makes hopping transport unlikely. There also is experimental evidence against the simple concept of a spin density wave.