Switching Spin Filling Sequence in a Bilayer Graphene Quantum Dot through Trigonal Warping

Area of Science:

• Condensed matter physics
• Quantum dots
• Graphene electronics

Background:

• Bilayer graphene exhibits unique electronic properties due to its layered structure.
• Quantum dots confine electrons, leading to discrete energy levels (shells).
• Trigonal warping is an anisotropic effect in graphene's band structure.

Purpose of the Study:

• To demonstrate electrical control over electron shell structure in bilayer graphene quantum dots.
• To investigate the role of trigonal warping in electron shell filling.
• To explore the manipulation of electron spin degree of freedom.

Main Methods:

• Fabrication of bilayer graphene quantum dots.
• Application of perpendicular electric fields (electrical gating).
• Measurement of electron shell filling and spin polarization.

Main Results:

• A switchable electron shell structure was achieved by electrical gating.
• Under low fields, s shell filled with 2 spin-up and 2 spin-down electrons.
• Higher fields induced threefold degeneracy, allowing s shell to hold 12 electrons with controlled spin polarization.

Conclusions:

• The trigonal warping effect in bilayer graphene quantum dots can be electrically manipulated.
• This provides a method to control electron spin polarization.
• The findings open possibilities for electrical access to spin degrees of freedom in graphene-based devices.