Berlin 2015 – scientific programme

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PV: Plenarvorträge

PV XXVI

PV XXVI: Plenary Talk

Thursday, March 19, 2015, 14:00–14:45, H 0105

Two-dimensional materials beyond graphene: atomically thin semiconductors — •Tony F. Heinz — Stanford University and SLAC National Accelerator Laboratory, Stanford, CA 94305, USA

Graphene has attracted great attention because of its exceptional potential for novel science and technology. Recently, this interest has expanded to the much wider class of 2D materials that arise as layers of van-der-Waals crystals that exhibit weak interlayer coupling, but strong in-plane bonding. While preserving graphene's flexibility and tunability by external perturbations, this broader set of materials provides access to more varied electronic and optical properties. In particular, the semi-metallic system of graphene is now complemented by stable 2D layers that are insulators and semiconductors.

Here we review the properties of atomically thin layers of semiconductors in the family of transition metal dichalcogenides, MX2, where M = Mo, W and X = S, Se, Te. In the limit of atomically thin layers, these materials exhibit a transition from optically dark indirect-gap materials to bright direct-gap materials. The 2D layers display remarkably strong many-body interactions, with exciton binding energies of 100's of meV and stable charged excitons at room temperature. The materials also provide new possibilities for control of the valley character of charge carriers. In particular, the helicity of light allows the selection of one of the two energetically degenerate, but distinct K/K' valleys in the Brillouin zone. We will discuss these emergent properties, as well as new possibilities afforded by forming tailored heterostructures of these 2D semiconducting layers.