Quantum Monte Carlo study of magnetism and chiral d+id-wave superconductivity in twisted bilayer graphene

TL;DR

This study uses quantum Monte Carlo simulations to explore how electron interactions and twist angles influence chiral d+id-wave superconductivity in twisted bilayer graphene, revealing the importance of electron-phonon coupling and twist angle tuning.

Contribution

It provides the first large-scale, unbiased simulation demonstrating the dominance of chiral NN-d+id pairing and the impact of twist angle on superconductivity in twisted bilayer graphene.

Findings

Chiral NN-d+id pairing dominates superconductivity.

Electron-phonon coupling significantly enhances pairing.

Decreasing twist angle increases pairing correlations.

Abstract

We employ a large-scale, unbiased constrained-path quantum Monte Carlo method to systematically simulate the effective two-orbital Hubbard model for twisted bilayer graphene in order to gain deeper insight into the relationship between correlated states and the superconducting pairing mechanism in twisted bilayer graphene, as well as the influence of the twist angle on superconductivity. Initially, we investigate the modulation of superconductivity by nearest-neighbor attractive Coulomb interactions, demonstrating that electron-phonon coupling plays a significant role in the system. Our numerical results reveal that the superconducting state is dominated by chiral NN-d+id superconducting electron pairing symmetry, and that such nearest-neighbor attractive Coulomb interactions significantly enhance the effective long-range pairing correlation function of chiral NN-d+id wave. Then, we explore how the twist angle affects the superconducting state. Our results show that as the twist angle deviates downward from 1.08{\deg}, the effective pairing correlation function of the chiral NN-d+id wave increases substantially. Through these investigations, our numerical findings not only contribute to a more comprehensive understanding of strongly correlated systems such as twisted bilayer graphene, but also provide guidance for identifying twist-angle systems with potentially higher superconducting transition temperatures.