Colossal Electroconductance

An abrupt, colossal jump in conductance is observed at a critical electric field, E$_{c}$, in bilayer manganite, La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$, crystals exhibiting charge order below T$_{CO}$. The four-terminal conductance measured on an ab-plane facet jumps well over three orders-of-magnitude at 135 K for x=0.6 and a smaller amount for x=0.5. The very large conductance anisotropy isolates four-terminal measurements on opposite faces of our crystals, so the temperature rise due to the dissipation at E$_{c}$ can be quantitatively determined and ruled out as the cause. Detailed data for x=0.5 and t=1-T/T$_{CO}<$0.15 show that E$_{c}$ extrapolates linearly to zero at T$_{CO}$ ($\sim $221 K) with E$_{c}$/t$\sim $13500 V/m. Possible mechanisms are being explored.