Graphene plasmonics provides an excellent new platform for strong optical field confinement with relatively low damping. This enables new device classes for deep subwavelength metamaterials, single-photon nonlinearities and extraordinarily strong light-matter interactions [1].
The main problem thus far was that strong damping was observed [2]. Different reasons for the unexpected strong damping, such as many-body effects in graphene and impurity scattering, were proposed as possible explanations. This strong observed damping hindered the further development of graphene plasmonic devices.
Using van der Waals heterostructures [3] new methods to integrate graphene with other atomically flat materials have become available. Graphene encapsulated between two films of hexagonal boron nitride is an example of such a heterostructure and shows extremely high room temperature transport mobility of charge carriers, only limited by the scattering with acoustic phonons in the graphene [4].
We show results where we exploit scattering-type scanning near-field optical microscopy to image propagating plasmons in such high quality graphene devices encapsulated between boron nitride [5]. Frequency dispersion and particularly plasmon damping in real space is determined and we show that these high quality graphene samples show unprecedented low graphene plasmon damping combined with extremely strong field confinement. We identify the main damping channels to be intrinsic thermal phonons in the graphene [6] as well as dielectric losses in the boron nitride. The low obtained damping as well as the theoretical understanding of the damping mechanisms are the key for the development of graphene nano-photonic and nano-optoelectronic devices.
References
[1] F.H.L. Koppens et al., Nano Lett. 11, 3370 (2011).
[2] J. Chen et al., Nature 487, 77 (2012).
[3] A. K. Geim and I. V. Grigorieva, Nature 499, 419 (2013).
[4] L. Wang et al., Science 342, 614 (2013).
[5] A. Woessner, M.B. Lundeberg, Y. Gao et al., Nature Mat. (DOI: 10.1038/nmat4169) (2014).
[6] A. Principi et al., Phys. Rev. B 90, 165408 (2014).
achim.woessner@icfo.es