Nematic topological semimetal and insulator in magic-angle bilayer graphene at charge neutrality

Liu, Shang; Khalaf, Eslam; Lee, Jong Yeon; Vishwanath, Ashvin

doi:10.1103/physrevresearch.3.013033

Cited by 146 publications

(102 citation statements)

References 47 publications

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“…These results are in agreement with another atomistic calculation which found that only retaining Hubbard interactions can only yield insulating states at charge neutrality [57,58], and also continuum model Hartree-Fock calculations that break C 2 symmetry [55]. To overcome the limitations of the current approach, future research should investigate longer-ranged exchange interactions [51][52][53][54][55][56] and the influence of ordering tendencies with q = 0 which could give rise to alternative symmetry-breaking mechanisms such as valley [9] and rotational [24] symmetry.…”

Section: Discussionsupporting

confidence: 86%

“…Experimentally, the situation is not clear, however, with some experiments reporting semimetallic behavior near the magic angle [1,2,4], while others (for very similar twist angles) observe a strong insulating state [5]. These conflicting results could arise from different levels of strain in the samples: Liu et al [53] demonstrated that a C 3 broken-symmetry state that is stabilized by strain retains its semimetallic character because of the topological properties of the flat bands of tBLG.…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, accurate models of tBLG should capture both short-ranged and long-ranged electron-electron interactions. To achieve this, several groups used Hartree-Fock calculations based on a continuum model of the electronic structure [51][52][53][54][55]. While these calculations have yielded many useful insights, they do not capture atomic-scale interactions (such as on-site interactions within carbon p z orbitals) and often only include a few bands near the Fermi level with the effect of all other bands being described by an effective dielectric constant.…”

Section: Introductionmentioning

confidence: 99%

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Importance of long-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene

et al. 2021

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Electron-electron interactions are intrinsically long ranged, but many models of strongly interacting electrons only take short-ranged interactions into account. Here, we present results of atomistic calculations including both long-ranged and short-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene and demonstrate that qualitatively different results are obtained when long-ranged interactions are neglected. In particular, we use Hartree theory augmented with Hubbard interactions and calculate the interacting spin susceptibility at a range of doping levels and twist angles near the first magic angle to identify the dominant magnetic instabilities. At the magic angle, mostly antiferromagnetic order is found, while ferromagnetism dominates at other twist angles. Moreover, long-ranged interactions significantly increase the twist angle window in which strong correlation phenomena can be expected. These findings are in good agreement with available experimental data.

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Section: Discussionsupporting

confidence: 86%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Importance of long-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene

et al. 2021

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“…The Hartree potential widens the bands, as it shifts the energies at the

and

points of the moiré Brillouin zone (BZ) with respect to those at the

point ( 39 – 43 ). The inclusion of the exchange term in a full Hartree–Fock calculation leads to broken symmetry phases, with valley and/or spin polarization ( 44 – 47 ), among other possible phases (see also refs. 47 – 50 ).…”

Section: The Modelmentioning

confidence: 99%

“…The inclusion of the exchange term in a full Hartree–Fock calculation leads to broken symmetry phases, with valley and/or spin polarization ( 44 – 47 ), among other possible phases (see also refs. 47 – 50 ).…”

Section: The Modelmentioning

confidence: 99%

Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene

Cea

Guinea

2021

Proc. Natl. Acad. Sci. U.S.A.

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The polarizability of twisted bilayer graphene, due to the combined effect of electron–hole pairs, plasmons, and acoustic phonons, is analyzed. The screened Coulomb interaction allows for the formation of Cooper pairs and superconductivity in a significant range of twist angles and fillings. The tendency toward superconductivity is enhanced by the coupling between longitudinal phonons and electron–hole pairs. Scattering processes involving large momentum transfers, Umklapp processes, play a crucial role in the formation of Cooper pairs. The magnitude of the superconducting gap changes among the different pockets of the Fermi surface.

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Towards holographic flat bands

Grandi

Juričić

Landea

et al. 2021

J. High Energ. Phys.

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Motivated by the phenomenology in the condensed-matter flat-band Dirac systems, we here construct a holographic model that imprints the symmetry breaking pattern of a rather simple Dirac fermion model at zero chemical potential. In the bulk we explicitly include the backreaction to the corresponding Lifshitz geometry and compute the dynamical critical exponent. Most importantly, we find that such a geometry is unstable towards a nematic phase, exhibiting an anomalous Hall effect and featuring a Drude-like shift of its spectral weight. Our findings should motivate further studies of the quantum phases emerging from such holographic models.

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Nematic topological semimetal and insulator in magic-angle bilayer graphene at charge neutrality

Cited by 146 publications

References 47 publications

Importance of long-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene

Importance of long-ranged electron-electron interactions for the magnetic phase diagram of twisted bilayer graphene

Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene

Towards holographic flat bands

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