Kekulé superconductivity in twisted magic angle bilayer graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Superconductivity in twisted graphene remains a significant unsolved problem in physics.
• Recent experiments suggest Kekulé ordering in moiré graphene superconductors, motivating new theoretical approaches.

Purpose of the Study:

• To develop a microscopic theory for superconductivity in twisted bilayer graphene.
• To explain the observed Kekulé ordering and other experimental signatures in moiré graphene superconductors.

Main Methods:

• Development of a microscopic theory for superconductivity.
• Analysis of pairing mechanisms, symmetry breaking, and quasiparticle density of states.
• Comparison of theoretical predictions with experimental data.

Main Results:

• Identification of an intra-valley, finite-momentum pair-density wave (PDW) with intrinsic Kekulé modulation.
• Observed features include C3 rotation symmetry breaking (nematic order), triplet pairing, and a evolving quasiparticle density of states.
• The proposed state aligns with experimental signatures and is near a BEC-like phase, explaining short coherence lengths.

Conclusions:

• A microscopic intra-valley Kekulé PDW is a compelling candidate for unconventional superconductivity in twisted graphene.
• The theory provides a unified explanation for multiple experimental observations.
• Further research can explore the implications of this PDW state for other moiré systems.