Fysiikan tutkimusseminaari

Abstract:

Twisted honeycomb lattices provide a versatile platform to engineer metamaterials with novel emergent properties. In these structures, the resulting geometric moire superlattice induces long-wavelength modulations that rearrange the electronic spectrum into minibands. Paradigmatic realizations are graphene on hexa-boron nitride (G/hBN) and twisted bilayer graphene (TBG). Firstly, for G/hBN-like systems [1], we will analyze all symmetry-allowed modulations and systematically classify the parameter space via gap-closing transitions in the low-energy spectrum. We will find criteria for protected degeneracies and for (valley) topological band gaps. Secondly, for TBG [2], we will see that tuning the twist angle to 𝛼∗ ≈ 0.8◦ generates flat bands away from charge neutrality that have a magnetic instability at half-filling. We will find that the magnetic correlations can be tuned electrically by applying an interlayer bias. Our results exemplify a powerful playground to control the topological and magnetic properties of graphene by means of moire engineering.

[1] T. M. R. Wolf, O. Zilberberg, I. Levkivskyi, and G. Blatter, Physical Review B 98, 125408 (2018)
[2] T. M. R. Wolf, J. L. Lado, G. Blatter, and O. Zilberberg, Physical Review Letters 123, 096802 (2019)