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Interaction-Induced Dirac Fermions from Quadratic Band Touching in Bilayer Graphene
Sumiran Pujari1, Thomas C Lang2, Ganpathy Murthy1
1Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506-0055, USA.
Physical Review Letters
|September 3, 2016
Summary
Local interactions in bilayer graphene models do not lead to strong coupling from a quadratic band touching (QBT). Instead, they create a Dirac phase, with antiferromagnetism emerging at a finite interaction strength.
Area of Science:
- Condensed Matter Physics
- Quantum Materials
- Theoretical Physics
Background:
- Bilayer graphene models exhibit quadratic band touching (QBT) at the charge neutrality point.
- The effect of local interactions on QBT is a subject of ongoing research and debate.
- Previous studies suggested weak interactions could flow to strong coupling at QBT.
Purpose of the Study:
- To investigate the impact of local interactions on the quadratic band touching (QBT) in Bernal honeycomb bilayer models.
- To resolve discrepancies regarding the behavior of weak interactions at QBT.
- To determine the phase diagram and critical behavior of interacting bilayer graphene systems.
Main Methods:
- Renormalization group (RG) arguments were employed to analyze the flow of interactions.
- Quantum Monte Carlo (QMC) simulations of the Hubbard model were performed.
- Unbiased simulations were conducted to avoid artifacts.
Main Results:
- RG analysis predicts that weak interactions generate a linear dispersion, causing them to flow back to weak coupling.
- QMC simulations show antiferromagnetism emerging at a finite interaction strength (U/t).
- The transition to antiferromagnetism is continuous and consistent with (2+1)D Gross-Neveu criticality.
Conclusions:
- Generically, small local interactions in bilayer graphene models create a Dirac phase without symmetry breaking, even with an initial QBT.
- A finite-coupling phase transition exists from the Dirac phase to a symmetry-broken state.
- The findings challenge previous predictions and offer a new understanding of interacting QBT systems.
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