Giant nonlinear conductivity in an organic conductor with a sharp metal-insulator transition: β'-(BEDT-TTF)_3(HSO_4)_2

摘要

The title organic conductor, where BEDT-TTF is bis(ethylenedithio)tetrathia-fulvalene, undergoes a sharp metal-insulator transition at T_(MI)= 126 K, below which giant nonlinear conductivity accompanied by negative differential resistance (NDR) is observed. In the usual organic conductors, resistance in the high-current region decreases following the power of current, but the present system shows abrupt NDR. The extraordinary NDR is quantitatively explained by phenomenology based on the energy balance and attributed to the sharp phase transition at T_(MI). This type of nonlinear transport is called "transition" type in contrast to the conventional "activation" type. The transition type is also characterized by the negative temperature dependence of the threshold power. It is predicted that there is a possibility that oscillating voltage emerges, but chaotic output never appears in this type. The different shapes of the two-probe current-voltage characteristics and pulse responses are also interpreted in view of the small ratio of the low-conducting and high-conducting states.