Abstract
An anomalous increase of electric conduction with decreasing temperature was found in the current through Pb(Ti,Zr)O3 ferroelectric/SrTiO3 epitaxial heterostructures. Comparison with current-voltage characteristics of other ferroelectric epitaxial heterostructures and the analysis using the band diagram indicate that the current is tunneling through the pn junction formed by Pb(Ti,Zr)O3 and SrTiO3, which have been regarded as insulators so far.