On resonant tunneling in Nb-Nb<inf>2</inf>O<inf>5</inf>-diodes

Abstract

In Nb 2 O 5 adjacent (≤ 5 nm) to a metal, the hybridization of localized electrons with conduction electrons yields interface states, which exist up to the Fermi energy E F of the metal. These interface states can be classified in 2 groups: -Localized electrons between 1 and 5 nm in front of Nb have a long decay life time into the metal, so that exchange processes via these interface states are obstructed and show a correlation (image potential) energy ΔUx> 5 meV. -Adjacent to the metal (< 1 nm) exchange processes without ΔUxare possible. Thus an electric field is already shielded in front of the metal and such interface states are weakly superconducting. These interface states yield a resonant tunnel current which cannot be fitted by direct barrier tunneling and which is exponentially enhanced over direct tunneling, yielding: -A strong, symmetric increase of the tunnel current, above 10-40 meV (giant zero bias anomaly: GZBA). -Josephson and leakage currents and smearing out of structures in the tunnel current at voltages between 0 and 20 meV.