COLLOQUIUM: Transport through graphene : from suspended multi-terminal devices to graphene on new substrates

CIC nanoGUNE Seminars

Speaker

Prof. Alberto Morpurgo, University of Geneva

When

2013/10/07
13:00

Place

nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian

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**Host** : Jose M. Pitarke One of the goals of graphene research is to improve the quality of devices for both fundamental studies and practical applications. In practice, this means to understand and minimize sources of extrinsic disorder. Since graphene is only one atom thick and normally –especially for layers exfoliated from natural graphite- it has very high chemical purity and structural perfection, much of the disorder originates from external materials in proximity to graphene, such as the substrate or adsorbates. One strategy to improve the quality of graphene, therefore, is to remove the substrate and perform transport measurements on suspended samples. Indeed measurements of this type have shown that suspended graphene has the highest possible quality. Unfortunately, for technical reasons, most suspended graphene devices have been realized in a two-terminal configuration, which limits the kind of experiments that are possible. In the first part of the talk I will show how multi-terminal suspended devices of very high-quality can be realized, and how they can be used to reveal new phenomena. In particular, I will discuss the observation of fractional quantum Hall effect in suspended multi-terminal bilayer graphene devices, with one of the most pronounced states occurring at even denominator filling of 1/2 , possibly being an experimental realization of a Moore-Read state. In the second part of the talk, I will discuss attempts to improve the quality of graphene on substrate, by using new materials. Specifically, I will discuss the case of SrTiO3 substrates, having dielectric constant approximately 1000 times larger than SiO2, and of h-BN substrates. Systematic studies on these substrates provide important new information. Specifically, we can conclude directly from the data that the microscopic mechanism that limits the mobility is also responsible for the carrier non- homogeneity that is observed in the experiments. Our analysis also strongly suggests that this mechanism is related to the presence of strain in the graphene layers.