Two-electron multiplets in bilayer graphene quantum dots*

Graphene quantum dots (QDs) are considered promising candidates for spin and valley-based quantum computing [1]. Here, we report on finite bias spectroscopy measurements of the two-electron spectrum in a gate defined bilayer graphene (BLG) QD for varying magnetic fields. The spin and valley degree of freedom in BLG give rise to a rich magnetic field dependent spectrum. We find that the two-electron states are split into multiplets of 6 orbital symmetric and 10 orbital anti-symmetric states, which are separated by 0.4 – 0.8 meV [2]. The symmetric multiplet exhibits an additional splitting due to short- range lattice scale interactions. With the help of detailed calculations, we are able to determine that inter-valley scattering and ‘current-current’ interaction constants are of the same magnitude in BLG [3, 4]. Understanding the two-particle spectrum in BLG QDs is an essential step for further investigating mechanisms of Pauli blockade in double QDs and eventually for identifying a suitable regime for qubit operations.

 

 

References

 

1. [1] B. Trauzettel et. al., Nature Physics 3, 192-196 (2007)
   
   [2] S. Möller et. al, arXiv:2106.08405 (2021)
   
   [3] A. Knothe et. al., arXiv:2104.033, (2021)
   
   [4] Y. Lemonik et. al., Phys. Rev. B 85, 24545 (2012)