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Transport through suspended graphene devices

27/05/2013, Prof. Alberto Morpurgo, from the University of Geneva


The experimental investigation of the intrinsic transport properties of graphene requires that all extrinsic sources of disorder affecting this material are eliminated. Disorder is caused mainly by most other materials, like the supporting substrate or adsorbates, that are in direct contact with graphene itself. Therefore, eliminating this disorder requires that graphene is suspended on top of a gate electrode and properly cleaned. The realization of suspended graphene devices represents an important breakthrough that has been demonstrated a few years ago, and that has led to a number of remarkable observations. In this talk, after a general introduction to the problem and to work done in the past, I will discuss progress on suspended graphene devices that is resulting from research done in our laboratory. This includes the investigation of suspended graphene ribbons, and, more recently, the realization of very high quality multi-terminal devices. First experiments on this new type of multi-terminal devices have allowed the direct observation of ballistic transport, and of the fractional quantum Hall effect in bilayer graphene. An unexpected result is the occurrence of a fractional quantum Hall state at an even denominator filling factor n=1/2. This is particularly interesting, because in most cases the fractional quantum Hall effect occurs at odd denominator states. Even denominator fractional quantum Hall effect had so far been observed only in two-dimensional electron gases hosted in very top quality GaAs heterostructures and is not understood theoretically.