Spectroscopic signatures of many-body correlations in magic angle twisted bilayer graphene

TL;DR

This study provides direct spectroscopic evidence of strong many-body electron-electron correlations in magic angle twisted bilayer graphene, revealing features that challenge mean-field models and highlighting the importance of complex interactions in its superconducting and insulating states.

Contribution

It offers the first direct spectroscopic evidence of many-body correlations in MATBG and demonstrates the failure of mean-field models, supporting the relevance of extended Hubbard models.

Findings

Unusual spectroscopic features attributed to electron-electron interactions.

Mean-field models cannot explain the observed spectroscopic characteristics.

Extended Hubbard model reproduces experimental spectroscopic features.

Abstract

The discovery of superconducting and insulating states in magic angle twisted bilayer graphene (MATBG) has ignited considerable interest in understanding the nature of electronic interactions in this chemically pristine material system. The phenomenological similarity of the MATBG transport properties as a function of doping with those of the high-Tc cuprates and other unconventional superconductors suggests the possibility that MATBG may be a highly interacting system. However, there have not been any direct experimental evidence for strong many-body correlations in MATBG. Here we provide such evidence from using high-resolution spectroscopic measurements, as a function of carrier density, with a scanning tunneling microscopy (STM). We find MATBG to display unusual spectroscopic characteristics that can be attributed to electron-electron interactions over a wide range of doping, including when superconductivity emerges in this system. We show that our measurements cannot be explained with a mean-field approach for modeling electron-electron interaction in MATBG. The breakdown of a mean-field approach for understanding the properties of other correlated superconductors, such as cuprates, has long inspired the study of highly correlated Hubbard model. We show that a phenomenological extended Hubbard model cluster calculation, motivated by the nearly localized nature of the relevant electronic states of MATBG produces spectroscopic features similar to those we observe experimentally. Our findings demonstrate the critical role of many-body correlations in understanding the properties of MATBG.