PRESSURE-DEPENDENCE OF CONDUCTIVITY AND MAGNETOCONDUCTANCE IN ION-IRRADIATED POLYIMIDE

The effect of pressure (up to 15 kbar) and magnetic field (up to 8 T) on the low-temperature (down to 1.3 K) DC conductivity and magnetocond uctance (MC) of ion-irradiated (Ar+ and Ga+ ions) polyimide films with a room-temperature conductivity sigma(300 K) of 200- 400 S cm(-1) has been investigated. It was shown that for samples on the metal side of the metal-insulator transition with the resistivity ratio rho(r) simi lar or equal to rho(1.3 K)/rho(300 K) = 1.8-2.3 the application of pre ssure increases sigma(300 K) by a factor of 2-3 with respect to that a t ambient pressure and the value of rho is slightly reduced. The low-t emperature conductivity shows a T-1/3 dependence. The sign of the MC a t ambient pressure is negative at all fields, thus implying that the c ontribution for the electron-electron interaction is dominant. However , at 15 kbar a positive MC at low fields, in both the transverse and t he longitudinal directions to the field, has been observed. This impli es that under pressure the system is more metallic with respect to tha t at ambient pressure, and the positive MC due to the dominance of the weak-localization contribution is enhanced by making the system more metallic under pressure.