Speaker: Pablo Ordejón
Affiliation: ICN2, Spain
Abstract Details: Graphene is a new material which holds the promise of revolutionizing technology areas such as electronics, due to its amazing properties. A large amount of activity is now being devoted to determining the effect of chemical functionalization of graphene on its electronic transport properties. The use of first-principles (ab-initio) methods is not straightforward to tackle these problems, since the relevant sizes involved in transport in graphene devices are much larger than those that ab-initio methods can reach. In this talk, I will describe how we are dealing with this problem, by using Density Functional Theory (DFT) calculations to build accurate effective Tight Binding models. These TB models are then used to compute the transport properties in mesoscopic samples by means of an efficient Kubo formulation based on wave packet evolution. In this talk, I will present the results of applying such an approach to graphene functionalized with oxygen and hydrogen. In the first case, we find that a metal-insulator transition can be driven as a function of the concentration of oxygen impurities, explaining recent experimental data. For the case of hydrogen, we have found that the electronic transport is closely linked with the magnetic ordering induced by the presence of hydrogen. In particular, it should possible to obtain measurable magnetoresistance signals by applying a sufficiently large magnetic field, which would pinpoint the presence of localized spins in H-functionalized graphene. Such effects are due to electron correlations in graphene, which translate into magnetic order and distinct transport properties of the different magnetic phases. I will also address the issue of transport in extremely disordered, amorphized graphene, which I will show to be an Anderson insulator with localization lengths of the order of only a few nanometers.

About The Speaker: Prof. Pablo Ordejón is the Director of the Catalan Institute of Nanotechnology (ICN) (Barcelona, Spain), as well as the leader of the Simulation and Theory Group at that institute.  His research has focused on the development of efficient methods for electronic structure calculations in large and complex systems, contributing to the development of techniques for large scale atomistic  simulations based on first principles methods like SIESTA. He has also been involved in the study of the fundamental properties of materials at the atomistic level. His current interests include, among many others, electronic transport in nanoscale devices and electronic processes at surfaces. He maintains frequent collaborations with industrial laboratories on the simulation of materials processes at the atomic level.

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