Fifteen Eighty Four

When Andre Geim and Konstantin Novoselov were preparing their first report on graphene back in 2004 [1], few would have imagined the impact that their paper would have today.

Indeed, the story of graphene is remarkable for many reasons. Because of the interesting science that it allowed to explore. Because of the speed with which it spread among laboratories worldwide and with which it rapidly transcended physics to reach materials science, engineering and beyond. Because it signaled a change in the dynamics of research in the related areas and the narrowing of the gap between basic and applied science.

But during this last decade, graphene has not been alone in the stardom of new materials. Soon after its discovery, a theoretical study opened the doors of what we call today topological insulators, a new class of materials defying the usual classification in terms of metals, semiconductors and insulators. The original proposal pointed to a realization in graphene but the spin-orbit interaction proved to be too weak for practical realizations. Later on, the full potential was unleashed in different materials propelling topological insulators as one of the new stars in condensed matter physics.

But physicists like unity and thus different proposals aim at endowing graphene with topological states, thereby bringing together the worlds of graphene and topological insulators. One of them started a few years ago and targets the use of light [2,3] as a mean to modify the electronic structure of the material to induce properties akin those of topological insulators [4].

Another trend is the use of defects or a substrate to enhance graphene’s spin-orbit coupling [5,6,7].  Using different chemical species on top of graphene [5] or placing graphene on top of islands of heavy materials like Pb [6] one may introduce regions where the stronger spin-orbit coupling could allow for much sough-after topological states. Now, a study appearing in the arxiv [8] provides new insights on the origin and strength of the spin-orbit coupling induced in graphene on transition metal dichalcogenides. The induced spin-orbit interaction in graphene by proximity effect  (and detected through weak antilocalization measurements) is found to be about two orders of magnitude larger than in pristine graphene.

This seems to be a promising start for the design of novel heterostructures with tailored spin-orbit coupling. The surprises and twists in the story of the wonder-material do not seem to stop, not even now that graphene is about to turn twelve.

[1] K. S. Novoselov et al. Science 306, 666 (2004)

[2] T. Oka and H. Aoki, “Photovoltaic Hall effect in graphene”, Phys. Rev. B 79, 081406(R) (2009).

[3] N. H. Lindner, Gil Refael, and V. Galitski, “Floquet topological insulator in semiconductor quantum wells”, Nature Physics 7, 490 (2011).

[4] P. M. Perez-Piskunow et al., Phys. Rev. B 89, 121401(R) (2014); L. E. F. Foa Torres et al., Phys. Rev. Lett. 113, 266801 (2014); M. A. Sentef et al., Nature Communications 6, 7047 (2015).

[5] A. Cresti et al. Phys. Rev. Lett. 113, 246603 (2014)

[6] F. Calleja et al. Nature Physics 11, 43–47  (2015)

[7] M. Gmitra and J. Fabian, Phys. Rev. B 92, 155403  (2015)

[8] Zhe Wang  et al. arXiv:1606.01789 [cond-mat.mes-hall] (2016)