Tunable giant valley splitting in edge-free graphene quantum dots on boron nitride

Graphene, the first two-dimensional material, provides two extra binary degrees of freedom, sublattice and valley, which are adequately described as pseudospins. These degrees might offer additional possibilities for information processing. Via low-temperature STM measurements, I will demonstrate the control of the valley degree of freedom within an edgeless quantum dot (QD) of graphene on BN. The QD is induced by the potential of the STM tip in combination with an external B field, which provides the required gaps by Landau quantization [1]. As such, the QD can be moved freely across the graphene/BN sample. The laterally changing orientation of the C atoms of graphene with respect to the B and N atoms of hBN changes the valley splitting of the confined state continuously [2]. This eventually leads to a tunable inversion of the valley splitting on nm length scales. Besides, I provide calculations based on density functional theory combined with a tight binding model, which excellently fit the experimental data revealing the possibility to use atomic interactions by adequate stacking of materials to control electronic degrees of freedom.
Additionally, I will pinpoint to the possibility to control the sublattice degree of freedom by pseudomagnetic fields [3].
[1] N. Freitag et al., Nano Lett., 16, 5798 (2016).
[2] N. Freitag et al., arXiv:1708.091070 (2017).
[3] A. Georgi et al., Nano Lett., 17, 2240 (2017).