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Jeudi 24 Avril 2014, 14h
Amphi Holweck, Esc C, 1ème etage
Negative Differential Conductivity and Coherent Tunneling transport in graphene-hBN-graphene structures.
Luis Brey
Instituto de Ciencia de Materiales de Madrid, CSIC, 28049 Madrid.
Similar techniques used for isolating graphene layers have been also applied to obtain two-dimensional crystal structures of highly anisotropic materials as hexagonal Boron Nitride (hBN) or transition metal dichalcogenides. Once isolated, atomic layers of different two-dimensional crystals can be reassembled layer by layer to create heterostructures with the designed electrical properties. This has opened a new field named graphene based Van der Walls heterostructures.
In this presentation I consider two graphene layers separated by an hBN monolayer. Graphene layers are twisted different angles with respect the hBN layer. The twisting produces a modulation in the hopping amplitude between the graphene layers that allow the existence of coherent tunneling, momentum and energy conserved, between the layers. As function of the bias voltage, we find a strong peak in the current density. The origin of this peak is the resonant tunneling from the Dirac cone of a graphene layer to the rotated Dirac cones in the opposite layer. A magnetic field applied parallel to the layers shifts the position of the rotated Dirac cones in the reciprocal space, and the peak in the current splits in three peaks. The observation of this splitting is an indication of the coherent nature of the negative differentia conductivity.