Probing two-electron multiplets in bilayer graphene quantum dots

TL;DR

This study investigates the two-electron energy spectrum in bilayer graphene quantum dots, revealing orbital multiplet structures, energy splittings, and the role of lattice interactions through combined experimental and theoretical analysis.

Contribution

It provides new insights into the orbital multiplet structure and lattice interactions in bilayer graphene quantum dots, supported by both spectroscopy measurements and theoretical modeling.

Findings

Orbital symmetric states are lower in energy than anti-symmetric states by 0.4-0.8 meV.

Symmetric multiplet states show an additional splitting of 0.15-0.5 meV.

Inter-valley scattering and current-current interactions are of comparable magnitude.

Abstract

We report on finite bias spectroscopy measurements of the two-electron spectrum in a gate defined bilayer graphene (BLG) quantum dot for varying magnetic fields. The spin and valley degree of freedom in BLG give rise to multiplets of 6 orbital symmetric and 10 orbital anti-symmetric states. We find that orbital symmetric states are lower in energy and separated by $\approx 0.4 - 0.8$ meV from orbital anti-symmetric states. The symmetric multiplet exhibits an additional energy splitting of its 6 states of $\approx 0.15 - 0.5$ meV due to lattice scale interactions. The experimental observations are supported by theoretical calculations, which allow to determine that inter-valley scattering and 'current-current' interaction constants are of the same magnitude in BLG.