Fig. 1: Colossal decrease of resistivity in highly polarized ultrathin dielectrics.

a Schematic diagram of the potential energy profiles across SrTiO₃ (STO) with increasing flexoelectric polarization (P; white arrow). Red solid lines and black dashed lines indicate the effective tunnel barrier and Fermi level, respectively. Blue and green dashed lines indicate the conduction band minimum and valence band maximum for P = 0, respectively. b Resistance as a function of ∆φ, obtained by calculating tunneling conductance through a Wentzel–Kramers–Brillouin (WKB) approximation. We normalize the resistance by the value at ∆φ = 0, and assume the bandgap ∆_bg, original barrier height φ₀, and original barrier width d₀ to be 3.2 eV, 1.4 eV, and 3.9 nm, respectively. At ∆φ = 1.8 eV, the valence band maximum crosses the Fermi level, which causes an abrupt reduction in the resistance. The black dashed line indicates the result obtained by neglecting the valence band contribution. Source data are provided as a Source data file.