Resolving Intervalley Gaps and Many-Body Resonances in Moir\'e Superconductor

TL;DR

This study uses scanning tunneling microscopy and spectroscopy to explore the formation of correlated phases and gaps in magic-angle twisted trilayer graphene, revealing two distinct gaps with different temperature and magnetic field dependencies, linked to superconductivity and pseudogap phenomena.

Contribution

It uncovers the existence of two well-resolved gaps in MATTG, clarifies their origins, and connects them to correlated phases and topological models, advancing understanding of superconductivity in moiré materials.

Findings

Discovery of two gaps within the superconducting doping range.

Outer gap persists at high temperatures and magnetic fields.

Inner gap closely follows doping behavior and remains resilient to structural variations.

Abstract

Magic-angle twisted multilayer graphene stands out as a highly tunable class of moir\'e materials that exhibit strong electronic correlations and robust superconductivity. However, understanding the relations between the low-temperature superconducting phase and the preceding correlated phases established at higher temperatures remains a challenge. Here, we employ scanning tunneling microscopy and spectroscopy to track the formation sequence of correlated phases established by the interplay of dynamic correlations, intervalley coherence, and superconductivity in magic-angle twisted trilayer graphene (MATTG). We discover the existence of two well-resolved gaps pinned at the Fermi level within the superconducting doping range. While the outer gap, previously associated with pseudogap phase, persists at high temperatures and magnetic fields, the newly revealed inner gap is more fragile in line with superconductivity MATTG transport experiments. Andreev reflection spectroscopy taken at the same location confirms a clear trend that closely follows the doping behaviour of the inner gap, and not the outer one. Moreover, spectroscopy taken at nanoscale domain boundaries further corroborates the contrasting behavior of the two gaps, with the inner gap remaining resilient to structural variations, as expected from the finite superconducting coherence length. By comparing our findings with recent topological heavy-fermion models, we identify that the outer gap originates from the splitting of the Abrikosov-Suhl-Kondo resonance due to the breaking of the valley symmetry arising from correlation-driven effects. Our results suggest an intricate but tractable hierarchy of correlated phases in twisted multilayer graphene.