Nonlinear conductivity of organic conductors is explained quantitatively starting from a phenomenological energy-balance equation. Experimental results of ͑TMET-TTP͒ 4 PF 6 are presented, where TMET-TTP is 2-͓4, 5-bis͑methylthio͒-1,3-dithiol-2-ylidene͔-5-͓4,5-ethylenedithio-1,3-dithiol-2-ylidene͔-1,3,4,6-tetrathiapentalene, and the simulation reproduces the nonlinear properties very well, including the voltage-current characteristics, power-law excess conductivity, and temperature dependence of the threshold field and current. The obtained heat capacity is much smaller than the lattice heat capacity, indicating unimportance of the Joule heating. Since the organic conductors show very little hysteretic switching, the time dependence of the energy balance is traced explicitly, defining nonlinear dynamics of hypothetical electron temperature, which reproduces oscillating states similar to that of the organic thyristor and even chaotic states under certain circumstances. It is expected that transient phenomena such as oscillatory and random outputs in some sort of organic and inorganic nonlinear conductors are quantitatively explained by this method, which in turn affords a playground of nonlinear dynamics.
The pressure dependence of resistivity for the checkerboard-type charge-ordered ͑CO͒ molecular conductor -͑meso-DMBEDT-TTF͒ 2 PF 6 has been investigated. Under the low pressure of 0.6 kbar, the temperature of resistivity minimum ͑T min ͒ falls from 90 K at an ambient pressure to 67 K, and after the resistivity has been increased, the superconducting ͑SC͒ transition is observed at 4.6 K. By applying magnetic field, the SC state is suppressed and the large positive magnetoresistance ͑MR͒ is demonstrated below T min in the CO state. Since the positive MR was observed even in the metallic state under high pressures, the summarized pressuretemperature ͑P − T͒ phase diagram reveals that the SC state neighbors to the CO-insulating and chargefluctuated metallic states.
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