Giant nonlinear conductivity and spontaneous current oscillation in an incommensurate organic superconductor.

Remarkable nonlinear conductivity is observed in the organic conductor (MDT-TS)(I2Br)_{0.420} (MDT-TS: 5H-2-(1,3-diselenol-2-ylidene)-1,3,4,6-tetrathiapentalene) below the metal-insulator transition at 30 K. This compound is characterized by the incommensurate donor and anion columns, and the non-Ohmic behavior is associated with the collective excitation at the antiferromagnetic insulating state. We have observed spontaneous current oscillation analogous to the organic thyristor found in the theta-phase organic conductor.