Nematic superconductivity in magic-angle twisted bilayer graphene from atomistic modeling

TL;DR

This paper uses atomistic modeling to reveal a highly inhomogeneous, nematic d-wave superconducting state in twisted bilayer graphene, characterized by local anisotropy, a full energy gap, and detectable local density of states variations.

Contribution

It demonstrates the importance of atomistic modeling in understanding superconductivity in TBG and uncovers a novel nematic d-wave pairing state with unique properties.

Findings

Nematic superconducting state with local anisotropy

Full energy gap despite d-wave symmetry

Detectable nematicity in local density of states

Abstract

Twisted bilayer graphene (TBG) develops large moir\'e patterns at small twist angles with flat energy bands hosting domes of superconductivity. The large system size and intricate band structure have however hampered investigations into the superconducting state. Here, using full-scale atomistic modelling with local electronic interactions, we find at and above experimentally relevant temperatures a highly inhomogeneous superconducting state with nematic ordering on both atomic and moir\'e length scales. The nematic state has a locally anisotropic real-valued d-wave pairing, with a nematic vector winding throughout the moir\'e pattern, and is three-fold degenerate. Although d-wave symmetric, the superconducting state has a full energy gap, which we tie to a {\pi}-phase interlayer coupling. The superconducting nematicity is further directly detectable in the local density of states. Our results show that atomistic modeling is essential and also that very similar local interactions produce very different superconducting states in TBG and the high-temperature cuprate superconductors.