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Shell Filling and Trigonal Warping in Graphene Quantum Dots
R Garreis1, A Knothe2, C Tong1
1ETH Zurich (Swiss Federal Institute of Technology in Zurich), 8093 Zurich, Switzerland.
Physical Review Letters
|April 23, 2021
Summary
Transport measurements in bilayer graphene quantum dots reveal electron shell filling governed by spin, valley, and minivalley degeneracies. These findings highlight the role of electron-electron interactions and band structure in few-electron systems.
Area of Science:
- Condensed matter physics
- Quantum electronics
- Materials science
Background:
- Bilayer graphene exhibits unique electronic properties due to its band structure.
- Quantum dots are nanoscale semiconductor structures that confine electrons.
- Understanding electron behavior in quantum dots is crucial for developing quantum technologies.
Purpose of the Study:
- To investigate the electronic transport properties of few-electron quantum dots in bilayer graphene.
- To explore the influence of spin, valley, and minivalley degeneracies on electron shell filling.
- To examine the role of exchange interactions in few-electron systems.
Main Methods:
- Fabrication of a few-electron circular quantum dot in bilayer graphene.
- Transport measurements of conductance resonances.
- Application of magnetic fields to probe spin-dependent effects.
- Band-structure calculations to model electronic states.
Main Results:
- Observed bunching of conductance resonances in groups of 4, 8, and 12, corresponding to spin, valley, and minivalley degeneracies.
- Demonstrated successive filling of 2D s and p shells with increasing electron numbers.
- Identified a transition to a threefold degenerate minivalley ground state for larger electron numbers.
- Confirmed Hund's second rule for spin filling, indicating significant exchange interactions.
Conclusions:
- The electronic shell filling in bilayer graphene quantum dots is dictated by a combination of spin, valley, and minivalley degeneracies.
- Electron-electron interactions, particularly exchange interactions, play a critical role in determining the ground state properties.
- The observed phenomena can be explained by the interplay between quantum confinement and the unique band structure of bilayer graphene.
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