Pulsed vs dc I-V measurements on AlxV1-xO2 (x = 0–0.013) single crystals: Unmasking a non-thermal electric field effect on these crystals

Abstract

The thermally induced insulator–insulator transition in Al-doped and the insulator–metal transition in doped as well as in pure VO2 single crystals are replicated in their dc I-V characteristics due to self-heating. In the investigation reported herein, self-heating (a lattice effect) was totally or almost totally avoided by using current pulses of millisecond durations, thus leaving the stage for electron heating. At low currents, the pulsed I-V are close to, or perfectly Ohmic, corresponding to the room temperature value of the resistance. Above a threshold, the voltage jumped backward and the current upward, marking a finite drop in resistance by 12%–24% for the different crystals; from there on, the resistance decreased linearly with the increasing voltage. Most R(V) traces were reproducible with small hysteresis upon increasing and decreasing currents. This behavior suggests an insulator-mixed-metal-insulator transition with metallic domains increasing with the increasing voltage (current). No reproducible behavior of the pulsed I-V characteristic of Al-doped crystals suggests onset of a non-thermal insulator–insulator transition. The interesting question now is what is the true nature of the material under the high pulsed voltage.