Current-controlled-negative-differential-resistivity, insulator to mixed metal-insulator state switching and power dissipation in self-heated VO₂ single crystals.

The outstanding features of the insulator-metal-transition (IMT) in VO₂ at T_IMT=340 K include a large negative thermal emissivity in the infrared over the transition. Under an applied current, the resistance drops due to Joule heating, the voltage reaches a maximum and a current controlled negative differential resistivity (CC-NDR) regime sets on. The mixed insulator-metal phase appears within the NDR regime. The stability of I(V) of a sample in this regime is governed by the load resistance (R_L) in series with the sample. For small enough R_L the sample switches from the last steady state with maximal Joule heating power (P_max) to a state with minimal Joule heating power (P_min). Instead of hot filaments that are formed upon switching in thin films, the mixed state of single crystals consists of dynamic or static metal-insulator domains with boundaries that cross the width of the crystal at favorable inclinations. The results derived from I-V characteristics of several VO₂ single crystals show that: 1. P_max / P_min may exceed by far the ratio between the emissivity in the infrared of the insulator to that of the metal and 2. Beyond the minimum, P increases with increasing current due to sliding domains but this increase as well as sliding are suppressed by damage.
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