Johannes H. J. Martiny: Tunable Valley Hall Effect in Graphene Superlattices

Johannes H. J. Martiny, Kristen Kaasbjerg, and Antti-Pekka Jauho Center for Nanostructured Graphene (CNG), DTU Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark johmar@nanotech.dtu.dk Valleytronics – the proposed field of information processing based on the electron valley index in e.g. graphene – relies on the control of protected valley currents [1]. In this work we consider the model of graphene gated via a periodic array of holes in a dielectric resting on a bottom electrode. We are inspired by the recent transport experiments in such structures [2]. Using tight‐binding supercell calculations and an unfolding procedure [3], we demonstrate how the electronic structure of this system corresponds to a gapped graphene structure with an associated valley Hall effect. We characterize the valley polarized currents by extracting the valley Hall conductivity from the unfolded Berry curvature of occupied states, and find that these currents become tunable by the gate‐potential. We furthermore perform Boltzmann conductivity calculations in order to characterize the valley Hall angle and make predictions for the indirect detection of such currents in nonlocal transport experiments when the Fermi level is tuned close to the band edge. Finally, we demonstrate the stability of the valley Hall effect in these systems when realistic potentials are considered which include the effect of disorder in the dielectric.   [1] J. R. Schaibley et al., Nature Reviews Materials, 1 (2016) 16055 [2] C. Forsythe et al., Nature Nanotechnology, 13 (2018) 566‐571 [3] T. Olsen and I. Souza, Physical Review B, 92 (2015) 125146 Johannes H. J. Martiny is a PhD student at DTU Physics in the group of Prof. Antti‐Pekka Jauho. He received his master degree in condensed matter theory from the Niels Bohr Institute at Copenhagen University in 2016. His current research interests include valley Hall effect in graphene superlattices, nonlocal signatures of topological currents in 2D materials, impurity‐induced magnetization in iron based superconductors, and Anderson localization of inter‐edge coupled edge states in 2D topological insulators.