Berlin 2008 – scientific programme

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SYNF: Symposium Ferroic materials and novel functionalities

SYNF 1: Ferroic materials and novel functionalities I

SYNF 1.10: Talk

Tuesday, February 26, 2008, 12:45–13:00, A 151

Ferroelectric Tunnel Junctions — •Hermann Kohlstedt¹, Nicholay Pertsev², Adrian Petraru¹, Ulrich Poppe¹, and Rainer Waser¹ — ¹Institut für Festkörperforschung and CNI, Forschungszentrum Jülich, Jülich, Germany — ²A. F. Ioffe Physico-Technical Institute, St. Petersburg, Russia

Quantum mechanical electron tunneling through nanoscale ferroelectric barriers is discussed for symmetric (identical electrodes) and asymmetric (dissimilar electrodes) junctions. It is shown that the lattice strains of piezoelectric origin modify the I-V relationship owing to strain-induced changes of the barrier thickness, electron effective mass, and position of the conduction-band edge. The effect of internal electric field caused by incomplete screening of polarization charges at the surfaces of a ferroelectric barrier is analyzed. For asymmetric junctions, this depolarizing-field effect also leads to a considerable change of the barrier resistance after the polarization reversal. The crossover between two types of hysteretic behavior is described taking into account both the strain and depolarizing-field effects. The results already obtained for these new types of tunnel junctions and the theoretical and experimental challenges existing in this area will be discussed. Experiments on the scaling properties of ultra-thin wedged BaTiO3 films will be presented. At the end we will provide an overview for the current status of the international studies of the so-called multiferroic tunnel junctions. By combing ferroelectric or multiferroic tunnel barriers with ferromagnetic and/or superconducting electrodes, a whole *zoo* of novel tunnel junctions can be proposed.