Nanoelectronics Vertical transport in stacked two dimensional systems

The discovery of graphene opened up a new research area: the study of two dimensional (2D) crystals. The family of 2D materials includes nowadays more than 10 materials and counting, The materials known so far display a huge variety of electronic properties, ranging from insulating (hexagonal boron nitride) to superconducting (NbSe2), including  semimetallic (graphene) and semiconducting (MoS2, WS2, MoSe2, WS2, black phosphorous). The 2D nature of these materials allows an unprecedented tuning of their properties, either by application of electric fields, mechanical deformations or chemical alteration. In the last three years, a new route to control material properties has emerged: the possibility of stacking different 2D materials on top of each other, creating new structures: van der Walls structures. These new structures have shown great promise for transistor and photodetector operation.

The goal of this project is to study electronic vertical transport in a variety of stacked 2D crystal structures, using realistic Hamiltonians derived from density functional calculations. The first system under study will consist of stacks of graphene and NbSe2 A particularly interesting question that will be addressed is how electronic order (superconducting and charge density wave) in the NbSe2 affects graphene. Vertical transport studies could shed light on this matter, and our calculations should serve as a guide to interpret future experimental results.

Prof. N. M. R. Peres, from the Center of Physics of the University of Minho (Braga, Portugal) is the external supervisor of this project.


Fig: Exemple of a vertical stack of 2D crystals: graphene sandwiching a few layers of a transition metal dichalcogenide (MoS2, WS2,...). By applying external gate and bias voltages, such device can operate both as a transistor or as a photodetector.