NONLINEAR TRANSPORT IN ALPHA-(BEDT-TTF)(2)I-3

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