Non-ohmic conduction electrical switching and magneto-resistance of quasi one-dimensional conductors at high pressures

Abstract

Electrical switching in the three charge?transfer complexes mtpa?(TCNQ)_x, benzidine–DDQ, and o?tolidine–DDQ has a common origin, and the basic features observed in these complexes are the same. Current–voltage (I–V) characteristics are analyzed on the basis of mobility variation with field, Schottky emission, Poole–Frenkel effect, and space?charge?limited current (SCLC). Non?ohmic conduction in these samples can be explained either by the Poole–Frenkel effect or by SCLC. Pulsed I–V measurements show the contribution of heating to the non?ohmic behavior. At high electric fields, of the order of 3 × 10? V cm?¹, the specimen switches from a low?conducting OFF state to a high?conducting ON state with ?_ON/?_OFF ? 10?–10?. Near the switching region, the voltage is unstable. The switching time recorded for the sample mtpa?(TCNQ)_x is 0.5 ms, which shows that the switching is a slow process. After switching, a region of differential negative resistance (DNR) with noise generation is observed in the I–V measurement. The instability in voltage vanishes if the current is reversed. Hysteresis observed in the I–V characteristic is reduced by repeating the measurement. Powder diffraction patterns of mtpa?(TCNQ)_x and its switched sample show structural changes. The temperature dependence of the switched mtpa?(TCNQ)_x sample down to helium temperature shows the characteristic of amorphous material, i.e., ln?? is proportional to T?¹?? (Mott’s variable?range hopping). The magnetoresistance of the ON state of mtpa?(TCNQ)_x obeys the classical behavior of metals and semiconductors. Thus, we conclude that the electrical switching observed in these three complexes is due to field?induced thermal switching, which leads to structural change.