Surface conduction on insulating BaTiO3 crystal suggesting an intrinsic surface electron layer

We report conduction measurements on the clean, free surface of transparent insulating BaTiO3 single crystals in high vacuum. We find that the insulat ing BaTiO3 crystals exhibit surface conductance that is dependent on the sp ontaneous polarization, whereas no conduction perpendicular to the surface is observed. The surface conduction shows semimetallic temperature dependen ce and persists down to at least 100 K. The observations suggest a two-dime nsional electron on a clean, free ferroelectric surface that may he regarde d as a ferroelectric metal. The results have important implications for und erstandings of the fundamental properties of ferroelectrics, the size effec t, and ferroelectric devices.