Quantized conductance in a contact between metallic oxide crystals

The conductance of a point contact between two crystals of metallic ${(\mathrm{L}\mathrm{a}}_{0.75}{\mathrm{Sr}}_{0.25}{)\mathrm{M}\mathrm{n}\mathrm{O}}_3$ shows steps as the contact is broken. A histogram of the conductance values observed in 60 breaks exhibits a series of sharp peaks at integer multiples of $G_0{=2e}^2/h.\mathrm{}$ Quantum conductance in these ceramics is qualitatively different from that normally seen in metals and suggests that no neck formation occurs during fracture of a contact between these brittle materials.