Jan-Philip Joost: Correlation Effects and the Topological Band Structure of Graphene Nanoribbon Heterojunctions

posted 28 May 2019, 10:23 by info admin
Jan-Philip Joost1, Antti-Pekka Jauho2, Michael Bonitz1
1Institute of Theoretical Physics and Astrophysics, University of Kiel, Germany
2CNG, DTU Physics, Technical University of Denmark

Topological insulators are a central theme in modern solid state physics as they combine an insulating bulk with robust in-gap boundary states. Recent progress in the atomically precise bottom-up synthesis of finite length graphene nanoribbons (GNRs) has opened up a new way to realize such topological materials.
The existence of localized in-gap states in heterojunctions of topologically distinct GNRs was predicted theoretically [1] and later confirmed experimentally [2]. It was found that GNRs composed of alternating segments of 7- and 9-armchair GNRs (AGNRs) exhibit new bulk bands and end states that differ qualitatively from the band structures of pristine 7- and 9-AGNRs. Most theoretical modelling of 7/9-ANGRs has been restricted to DFT/LDA or tight binding (TB) methods which are known to underestimate or completely ignore correlation effects, respectively. Since electronic correlations are known to be very important in GNRs [3], a quantitative analysis must go beyond these simple theories. Here, we present simulations of 7/9-AGNRs based on a Green functions method with second Born and GW self-energies [3] applied to an effective Hubbard model. We find remarkable quantitative agreement with the experimental local dI/dV measurements of Ref.[2]. Especially the description of the topological end states is greatly improved by the inclusion of correlations compared to the TB and LDA results.
Moreover, our approach can be easily extended to extract the transport properties of these systems.

[1] T. Cao et al., Phys. Rev. Lett. 119, 076401 (2017)
[2] D. J. Rizzo et al., Nature 560, 204-208 (2018)
[3] J.-P. Joost et al., Phys. Stat. Sol. (b) (2019), doi: 10.1002/pssb.201800498

Jan-Philip Joost is currently a Ph.D. student in the group of Michael Bonitz at the University of Kiel. He received his B.Sc. and M.Sc. in Physics at the University of Kiel. His research interest is the study of equilibrium properties as well as non-equilibrium electron dynamics in graphene nanostructures by means of nonequilibrium Green functions.