Nonlinear transport in Qn(TCNQ)₂

Abstract

A nonlinear electric field dependence is found in the quasi-one-dimensional organic conductor Qn(TCNQ),. The non-Ohmic behaviour sets in a t electric fields as low as 2 V/cm and it is observed to temperatures above 100 K. Results obtained on a series of crystals with different lengths show that in defect-free crystals the nonlinearity is intrinsic. Microscopic breaks enhance while chemical impurities depress the nonlinearities. The observations are in contradiction with a simple band semiconductor model and also with models where transport properties are assumed to be determined by short localization lengths.Es wird eine nichtlineare Feldabhangigkeit in den1 quasi-eindimensionalen organischen Leiter &n(TCN&), gefunden. Das nichtohmsche Verhalten tritt schon bei Feldstarken von 2 V/cm auf und ist bis zu Temperaturen iiber 100 K bemerkbar. Die Untersuchung an einer Serie von Kristallen verschiedener Lange zeigt, daB in defektfreien Kristallen die Nichtlinearitat cine innere Eigenschaft der Substanz ist. Mikroskopische Bruche vergroI3ern den Effekt, chemische Verunreinigungen dagegen vermindern ihn. Diese Beobachtungen steheii im Gegensatz zu einem einfaehen Band-Halbleitermodell und ebenso mit Modellen, in denen Transporteigenschaften durch kurze Lokalisationslangen bestimmt sind. l )

Electrical switching in benzidine-DDQ under pressure

“…Non-ohmic conduction and electrical switching is observed in many of the charge transfer complexes (Subramanyam and Hemamalini Naik 1985). Non-ohmic conduction observed in one-dimensional conductors TTF-TCNQ (Gunning and Heeger 1978), Qn-(TCNQ) z (Mihaly et al 1979), (TMTSF)2PF 6 (Chaikin et al 1980), NbSe 3 and TaS 3 (Fleming and Grimes 1979;Miller et al 1983) and (CH)x (Epstein et al 1980) was explained by depinning of charge density wave (CDW) by an applied electric field. Space charge limited current (Farges et al 1972), phononassisted hopping through random barriers (Lee and Rice 1979) and tunnelling of electrons through barriers in the conducting strands (Patrick and Rowland 1979) are also used to explain non-ohmic conduction.…”