Imaging inter-valley coherent order in magic-angle twisted trilayer graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Magic-angle twisted trilayer graphene (MATTG) is known for exhibiting complex electronic phases driven by strong correlations.
• These phases often involve spontaneous breaking of the material's inherent symmetries.

Purpose of the Study:

• To investigate the nature of correlated electronic phases in MATTG.
• To identify signatures of interaction-driven spatial symmetry breaking.
• To explore the relationship between atomic-scale reconstruction and longer-range order.

Main Methods:

• Scanning tunnelling microscopy (STM) was employed to probe the electronic properties of MATTG.
• Atomic-scale imaging and spectroscopy were used to observe lattice reconstruction and electronic gaps.
• Auto-correlation and Fourier analyses were applied to determine phase periodicity.
• Large-scale moiré maps were utilized to study spatial modulations.

Main Results:

• Observed atomic-scale reconstruction of the graphene lattice, forming a Kekulé supercell, associated with a correlated electronic gap.
• Identified spontaneous inter-valley coherence between electrons within the Kekulé structure.
• Revealed coexistence of atomic-scale reconstruction with translation symmetry breaking at the moiré scale.
• Found that moiré-scale modulations decrease with hole doping and are weakly dependent on magnetic fields.
• Results are consistent with theoretically proposed incommensurate Kekulé spiral order.

Conclusions:

• The study provides crucial insights into the correlated phases of MATTG, particularly concerning strain effects.
• Atomic-scale reconstruction and inter-valley coherence are key features of these correlated states.
• Superconductivity in MATTG may emerge from this inter-valley coherent parent state.