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Entropy Spectroscopy of a Bilayer Graphene Quantum Dot
C Adam1, H Duprez1, N Lehmann1
1ETH Zurich, Solid State Physics Laboratory, Zurich CH-8093, Switzerland.
Physical Review Letters
|October 5, 2025
Summary
Entropy measurements reveal new ground state properties in graphene quantum dots. This technique uncovers spin-orbit interactions and confirms the degeneracy of quantum states, offering a novel approach to studying quantum matter.
Area of Science:
- Condensed Matter Physics
- Quantum Information Science
- Materials Science
Background:
- Quantum dots in bilayer graphene are crucial for quantum computing.
- Entropy measurements offer thermodynamic insights beyond traditional transport measurements.
- Understanding ground state degeneracy is key to controlling quantum devices.
Purpose of the Study:
- To measure entropy changes during charge transitions in graphene quantum dots.
- To investigate the ground state degeneracy in one- and two-carrier regimes.
- To explore the potential of entropy measurements as a novel tool in quantum device characterization.
Main Methods:
- Electrostatically defined quantum dot fabrication in bilayer graphene.
- Measurement of entropy change during charge transitions.
- Application of out-of-plane magnetic fields.
Main Results:
- In the one-carrier regime, entropy confirmed a twofold ground state degeneracy, lifted by a magnetic field, aligning with transport data.
- In the two-carrier regime, entropy indicated a nondegenerate ground state at zero magnetic field, contradicting prior studies.
- A Kane-Mele-type spin-orbit interaction was identified as the cause for degeneracy lifting in the two-carrier system.
Conclusions:
- Entropy measurements are a valid and effective supplementary tool for probing quantum device ground state degeneracy.
- The study reveals a previously unobserved Kane-Mele-type spin-orbit interaction effect in graphene quantum dots.
- This entropy-based technique holds promise for the study of exotic quantum matter and fractional ground state entropies.
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