Engineering flat bands in twisted-bilayer graphene away from the magic angle with chiral optical cavities

Abstract

Twisted bilayer graphene (TBG) is a recently discovered two-dimensional superlattice structure which exhibits strongly-correlated quantum many-body physics, including strange metallic behavior and unconventional superconductivity. Most of TBG exotic properties are connected to the emergence of a pair of isolated and topological flat electronic bands at the so-called magic angle, $\theta \approx 1.05^{\circ }$, which are nevertheless very fragile. In this work, we show that, by employing chiral optical cavities, the topological flat bands can be stabilized away from the magic angle in an interval of approximately $0.8^{\circ }<\theta <1.3^{\circ }$. As highlighted by a simplified theoretical model, time reversal symmetry breaking (TRSB), induced by the chiral nature of the cavity, plays a fundamental role in flattening the isolated bands and gapping out the rest of the spectrum. Additionally, TRSB suppresses the Berry curvature and induces a topological phase transition, with a gap closing at the $\Gamma$ point, towards a band structure with two isolated flat bands with Chern number equal to $0$. The efficiency of the cavity is discussed as a function of the twisting angle, the light-matter coupling and the optical cavity characteristic frequency. Our results demonstrate the possibility of engineering flat bands in TBG using optical devices, extending the onset of strongly-correlated topological electronic phases in moiré superlattices to a wider range in the twisting angle.

v2: matching published version in PRL

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• Cavity-Vacuum-Induced Chiral Spin Liquids in Kagome Lattices: Tuning and Probing Topological Quantum Phases via Cavity Quantum Electrodynamics
• Quantum Hall effect in a chiral cavity
• Angular Momentum-Dependent Spectral Shift in Chiral Vacuum Cavities
• Cavity-Mediated Electron-Electron Interactions: Renormalizing Dirac States in Graphene
• Cavity Quantum Hall Hydrodynamics
• Dynamical nonlinear optical response in time-periodic quantum systems
• Vacuum induced three-body delocalization in cavity quantum materials
• General theory of cavity-mediated interactions between low-energy matter excitations
• Harnessing Vacuum Fluctuations to Shape Electronic and Photonic Behavior
• Spontaneous Symmetry Breaking of Cavity Vacuum and Emergent Gyrotropic Effects in Embedded moiré Superlattices
• Chern insulators and topological flat bands in cavity-embedded kagome systems
• Quantifying Twist Angles in Cuprate Heterostructures with Anisotropic Raman Signatures