Shell Filling and Trigonal Warping in Graphene Quantum Dots

Abstract

Transport measurements through a few-electron circular quantum dot in bilayer graphene display bunching of the conductance resonances in groups of four, eight and twelve. This is in accordance with the spin and valley degeneracies in bilayer graphene and an additional threefold 'minivalley degeneracy' caused by trigonal warping. For small electron numbers, implying a small dot size and a small displacement field, a two-dimensional s- and then a p-shell are successively filled with four and eight electrons, respectively. For electron numbers larger than twelve, as the dot size and the displacement field increase, the single-particle ground state evolves into a three-fold degenerate minivalley ground state. A transition between these regimes is observed in our measurements and can be described by band-structure calculations. Measurements in magnetic field confirm Hund's second rule for spin filling of the quantum dot levels, emphasizing the importance of exchange interaction effects.

10 pages, 7 figures

References in corpus (5)

• The electronic properties of bilayer graphene
• Intrinsic and Rashba Spin-orbit Interactions in Graphene Sheets
• Spin qubits in graphene quantum dots
• Excited states in bilayer graphene quantum dots
• Tunable few electron quantum dots in InAs nanowires

Cited by in corpus (6)

• Gate-Controlled Quantum Dots Based on Two-Dimensional Materials
• Valley current generation using biased bilayer graphene dots
• Gate-tunable regular and chaotic electron dynamics in ballistic bilayer graphene cavities
• Switching spin filling sequence in a bilayer graphene quantum dot through trigonal warping
• Tunable p-n junction barriers in few-electron bilayer graphene quantum dots
• Tuning confined states and valley g-factors by quantum dot design in bilayer graphene