Rapid voltage oscillations and ac-dc interference phenomena in the two-dimensional charge-ordered organic conductor β″-(bis(ethylenedithio)tetrathiafulvalene)3(ClO4)2

Abstract

Giant nonlinear conductivity and rapid voltage oscillations are investigated in a two-dimensional organic conductor β″-(BEDT-TTF)3(ClO4)2, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene. Below the metal-insulator transition temperature at TMI=170 K, remarkable negative differential resistance appears, where voltage oscillation with a frequency of 20–60 kHz is observed, and the frequency increases in proportion to the applied current. This phenomenon is reminiscent of narrow band noise originating from the sliding charge density waves in one-dimensional conductors, but the oscillation appears in two directions of the two-dimensional non-stripe charge order. The ac-dc interference phenomena are investigated; when alternating current is superposed, an anomalous jump appears in the current-voltage characteristics at the position where the applied frequency coincides with the internal frequency corresponding to the applied dc current. The jump is interpreted in analogy with the Shapiro steps in the ac Josephson effect, in which the step height changes following the first-order Bessel function of the applied ac current.