Novel physics in stacks of graphene and related 2D materials
Klaas-Jan Tielrooij (ICFO – Institute of photonic sciences (Spain))

Two-dimensional (2D) materials possess many remarkable physical properties. Graphene, for instance, has a gapless band structure with linear dispersion, flat absorption spectrum, strong carrier-carrier interactions and a large, tunable Seebeck coefficient. Hexagonal BN (hBN) is an insulator with a very similar lattice as graphene, while hosting hyperbolic phonon-polaritons, which are modes with an exceptionally high density of optical states. Stacking different 2D materials on top of each other, forming Van der Waals heterostructures with clean interfaces, allows for combining properties of different materials, as well as creating novel characteristics. For example, encapsulation of graphene by hBN leads to extremely high electrical conduction of graphene charge carriers [1].
In this talk, I will first discuss the ultrafast dynamics that occur in graphene after photoexcitation, in particular ultrafast carrier heating through interband and intraband carrier scattering processes [2]. Interestingly, these hot carriers can be exploited for creating a photovoltage on a femtosecond timescale in graphene-based photodetectors [3]. The second part is focused on the cooling dynamics of hot graphene carriers, where hBN-encapsulated graphene exhibits surprisingly efficient out-of-plane heat transfer, on a picosecond timescale, by coupling to hyperbolic modes [4]. These results will be put in perspective of their usefulness towards applications such as photodetection, data communication and heat management.
[1] A.K. Geim et al. Nature 499, 419 (2013), L. Wang et al. Science 342, 614 (2013)
[2] K.J. Tielrooij et al. Nature Phys. 9, 248 (2013), Z. Mics et al. Nature Comms. 6, 7655 (2015), A. Tomadin et al. to be submitted
[3] K.J. Tielrooij et al. Nature Nanotech. 10, 437 (2015), M. Massicotte et al. Nature Comm. 7, 12174 (2016)
[4] A. Principi et al. Phys. Rev. Lett. 118, 126804 (2017), K.J. Tielrooij et al. Arxiv 1702:03766 (2017)