SciPost Phys. 13, 040 (2022) ·
published 30 August 2022
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We study the possibility of charge order at quarter filling and antiferromagnetism at half-filling in a tight-binding model of magic angle twisted bilayer graphene.
We build on the model proposed by Kang and Vafek, relevant to a twist angle of $1.30^\circ$, and add on-site and extended density-density interactions.
Applying the variational cluster approximation with an exact-diagonalization impurity solver, we find that the system is indeed a correlated (Mott) insulator at fillings $\frac14$, $\frac12$ and $\frac34$.
At quarter filling, we check that the most probable charge orders do not arise, for all values of the interaction tested. At half-filling, antiferromagnetism only arises if the local repulsion $U$ is sufficiently large compared to the extended interactions, beyond what is expected from the simplest model of extended interactions.
SciPost Phys. 11, 017 (2021) ·
published 21 July 2021
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We apply cluster dynamical mean field theory with an exact-diagonalization
impurity solver to a Hubbard model for magic-angle twisted bilayer graphene,
built on the tight-binding model proposed by Kang and Vafek (2018), which
applies to the magic angle $1.30^\circ$. We find that triplet superconductivity
with $p+ip$ symmetry is stabilized by CDMFT, as well as a subdominant singlet
$d+id$ state. A minimum of the order parameter exists close to quarter-filling
and three-quarter filling, as observed in experiments.
Prof. Sénéchal: "1. The model we use does not e..."
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