Johannes H. J. Martiny: Berry curvature and valley Hall effect in nanostructured graphene

Phd Student, Department of Micro- and Nanotechnology, Technical University of Denmark Two-dimensional (2D) materials with hexagonal lattice structures host quasiparticles characterized by the so-called "valley pseudospin", which labels degenerate energy extrema in momentum space. This has led to proposals of information processing or "valleytronics" with the valley pseudospin serving as an analogue of the traditional electron spin in spintronics [1]. In order to realize valleytronic technology, a control scheme for manipulating the valley pseudospin must be constructed. Recently, the generation of a non-dissipative pure valley current has been reported in gated bilayer graphene [2]. The measured transverse current (or "valley Hall effect" in analogy with the spin Hall effect) can be theoretically predicted from the introduction of Berry curvature in the 2D systems by the applied electric field. The particular form of the Berry curvature in this system deflects electrons with different valley index in opposite directions, thereby generating a pure valley current. In this project we aim to introduce a similar effect by purely geometrical means. Berry curvature is generated by introducing a periodic array of vacancies in single-layer graphene, forming the so-called graphene antidot lattice (GAL) [3]. The shape of this antidot structure can then be engineered by numerical optimization to generate a similar pure valley current. This could potentially provide a means to control the valley pseudospin without the application of external fields. 1. X. Xu et al., Nature Physics 10, 343-350 (2014)  2. Y. Shimazaki et al., Nature Physics 11, 1032-1036 (2015) 3. T. G. Pedersen et al.,  Phys. Rev. Lett. 100, 136804 (2008)  Johannes H. J. Martiny has been a PhD student in the theoretical nanotechnology group at the Technical University of Denmark since February of this year, supervised by Prof. A.-P. Jauho and co-supervised by Researcher K. Kaasbjerg.   Prior to his PhD studies he received  B.S. ('14) and M.S. ('16) degrees in Physics from the Niels Bohr Institute at the University of Copenhagen, with the final two years spent conducting research in the field of high temperature superconductivity. His current research interests include the generation of valley Hall effect in 2D systems, topologically protected edge states, and the theoretical underpinning of density of states modulations around impurity atoms.