  In this paper, we present data for two nanocrystalline YBa2Cu3O7-x (YBCO)
samples which both exhibit Josephson-like Colossal Resistive Switching (JCRS)
in voltage-current (V-I) traces from 4.2 K up to room temperature, in magnetic
fields up to 8 T. We report Josephson-like hysteresis for both positive and
negative current that has not been observed before in colossal resistive
switching materials. Non-zero resistance was measured in transport measurements
at all temperatures. At low temperatures (< 90 K), we also observed the usual
properties for YBCO including weak superconducting and paramagnetic behavior,
measured using ac susceptibility and magnetization measurements. The
resistivity of these nanocrystalline samples is 3 orders of magnitude higher
than standard polycrystalline materials at 300 K and the temperature dependence
semiconductor-like. We cannot rule out the possibility that these materials
contain a superconducting component responsible for the JCRS behavior at room
temperature.
