Unconventional Superconductivity and Density Waves in Twisted Bilayer Graphene

Isobe, Hiroki; Yuan, Noah F. Q.; Fu, Liang

doi:10.1103/physrevx.8.041041

Cited by 375 publications

(296 citation statements)

References 54 publications

Supporting

Mentioning

282

Contrasting

Unclassified

Order By: Relevance

“…In this work, we reveal that the combination of the two aspects will bring about the TRS-breaking chiral SO(4) spincharge DW state with intriguing properties, whose energy is reasonably lower than that of the 3Q-CDW state proposed in Ref. [58]. Further more, our results are more different from those in Refs.…”

Section: Chiral So(4) Spin-charge Dwcontrasting

confidence: 87%

“…2(c), which verifies the isotropic CDW state as the energetically most favored CDW state, consistent with the so called 3Q CDW state defined in Ref. [58]. However, this 3Q-CDW state is beat by the non-coplanar chiral SDW state with ∆ (s)…”

Section: B Consequence Of Degeneracy Among Wave Vectorssupporting

confidence: 86%

“…Further more, our results are more different from those in Refs. [58,79] for the cases of J H 0 (which will be studied in the next section). Briefly, both Refs.…”

Section: Chiral So(4) Spin-charge Dwmentioning

confidence: 99%

“…the U(1)-valley symmetry. This symmetry is maintained even as electronelectron interactions are considered [36,46,52,58,79,[89][90][91]. What's more, each valley independently supports an spin-SU(2) symmetry in the level of band structure, leading to the SU(2)⊗SU(2) symmetry.…”

mentioning

confidence: 99%

“…Hund-like (anti-Hund-like) inter-valley exchange interaction which leads to the SDW (CDW) and triplet p + ip (singlet d + id) SC [58,79]. These viewpoints, however, neglect a key ingredient, i.e.…”

mentioning

confidence: 99%

See 4 more Smart Citations

Chiral Spin Density Wave and d+id Superconductivity in the Magic-Angle-Twisted Bilayer Graphene

et al. 2018

View full text Add to dashboard Cite

Starting from a realistic extended Hubbard model for a p x,y -orbital tight-binding model on the Honeycomb lattice, we perform a thorough investigation on the possible electron instabilities in the magic-angle-twisted bilayer-graphene near the van Hove (VH) dopings. Here we focus on the interplay between the two symmetries of the system. One is the approximate SU(2)×SU(2) symmetry which leads to the degeneracy between the inter-valley spin density wave (SDW) and charge density wave (CDW) as well as that between the inter-valley singlet and triplet superconductivities (SCs). The other is the D 3 symmetry, which leads to the degeneracy and competition among the three symmetry-related wave vectors of the density-wave (DW) orders, originating from the Fermi-surface nesting. The interplay between the two degeneracies leads to intriguing quantum states relevant to recent experiments, as revealed by our systematic random-phase-approximation based calculations followed by a succeeding mean-field energy minimization for the ground state. At the SU(2)×SU(2) symmetric point, the degenerate inter-valley SDW and CDW are mixed into a new state of matter dubbed as the chiral SO(4) spin-charge DW. This state simultaneously hosts three 4-component vectorial spin-charge DW orders with each adopting one wave vector, and the polarization directions of the three DW orders are mutually perpendicular to one another in the R 4 space. In the presence of a tiny inter-valley exchange interaction with coefficient J H → 0 − breaking the SU(2)×SU(2) symmetry, a pure chiral SDW state is obtained. In the case of J H → 0 + , although a nematic CDW order is favored, two SDW orders with equal amplitudes are accompanied simultaneously. This nematic CDW+SDW state possesses a stripy distribution of the charge density, consistent with the recent STM observations. On the aspect of SC, while the triplet p+ip and singlet d+id topological SCs are degenerate at J H = 0 near the VH dopings, the former (latter) is favored for J H → 0 − (J H → 0 + ). In addition, the two asymmetric doping-dependent behaviors of the superconducting T c obtained are well consistent with experiments. * yyzhang@bit.edu.cn † yangfan blg@bit.edu.cn sity wave (DW). If the doping level deviates from the DW ordered regime, the short-ranged DW fluctuations would mediate the SC, which proposes two questions: what type of the spin or/and charge DW would be driven by the FS-nesting and VHS, and what is the pairing symmetry mediated by the DW fluctuations?These questions associate with the special symmetry of the MA-TBG, which lies in the valley degree of freedom. The continuum theory [66] suggests that the electron states within the two different MBZs centered at K and K would not hybridize for small twist angle, resulting in a conservation law for the valley degree of freedom, i.e. the U(1)-valley symmetry. This symmetry is maintained even as electronelectron interactions are considered [36,46,52,58,79,[89][90][91]. What's more, each valley independently supports an spin-SU(2) symmetry i...

show abstract

Section: Chiral So(4) Spin-charge Dwcontrasting

confidence: 87%

Section: B Consequence Of Degeneracy Among Wave Vectorssupporting

confidence: 86%

“…Further more, our results are more different from those in Refs. [58,79] for the cases of J H 0 (which will be studied in the next section). Briefly, both Refs.…”

Section: Chiral So(4) Spin-charge Dwmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Chiral Spin Density Wave and d+id Superconductivity in the Magic-Angle-Twisted Bilayer Graphene

et al. 2018

View full text Add to dashboard Cite

show abstract

Cataloging High‐Quality Two‐Dimensional van der Waals Materials with Flat Bands

Duan,

Ma,

Zhang

et al. 2024

Adv Funct Materials

View full text Add to dashboard Cite

Benefited from the lower dimensionality compared to their 3D counterpart, 2D flat‐band systems provide cleaner lattice models, easier experimental verification, and higher tunability, which make the 2D van der Waals (vdW) system an ideal playground for exploring flat‐band physics as well as their potential applications. Given the vast amount of research in the field of flat bands, a simple and efficient approach to search for realistic vdW materials with flat bands is still missing. Here, a two‐tier framework to filter and diagnose high‐quality flat‐band vdW materials by combining high‐throughput first‐principles calculations and the proposed 2D flat‐band score criterion is presented. Based on systematic geometrical analysis, 861 potential monolayer vdW materials are initially obtained amounting to 187,093 structures as stored in the Inorganic Crystal Structure Database. By applying the 2D flat‐band score criterion, 229 flat‐band candidates are efficiently identified, among which a sub‐catalog of 74 materials with flat bands right next to the Fermi level is further provided to facilitate experimental verification. All these efforts to screen experimentally available flat‐band candidates will certainly motivate continuing exploration toward the realization of this class of special materials and their applications in material science.

show abstract

Observation of Electrically Tunable van Hove Singularities in Twisted Bilayer Graphene from NanoARPES

et al. 2020

View full text Add to dashboard Cite

The possibility of triggering correlated phenomena by placing a singularity of the density of states near the Fermi energy remains an intriguing avenue toward engineering the properties of quantum materials. Twisted bilayer graphene is a key material in this regard because the superlattice produced by the rotated graphene layers introduces a van Hove singularity and flat bands near the Fermi energy that cause the emergence of numerous correlated phases, including superconductivity. Direct demonstration of electrostatic control of the superlattice bands over a wide energy range has, so far, been critically missing. This work examines the effect of electrical doping on the electronic band structure of twisted bilayer graphene using a back‐gated device architecture for angle‐resolved photoemission measurements with a nano‐focused light spot. A twist angle of 12.2° is selected such that the superlattice Brillouin zone is sufficiently large to enable identification of van Hove singularities and flat band segments in momentum space. The doping dependence of these features is extracted over an energy range of 0.4 eV, expanding the combinations of twist angle and doping where they can be placed at the Fermi energy and thereby induce new correlated electronic phases in twisted bilayer graphene.

show abstract

Unconventional Superconductivity and Density Waves in Twisted Bilayer Graphene

Cited by 375 publications

References 54 publications

Chiral Spin Density Wave and d+id Superconductivity in the Magic-Angle-Twisted Bilayer Graphene

Chiral Spin Density Wave and d+id Superconductivity in the Magic-Angle-Twisted Bilayer Graphene

Cataloging High‐Quality Two‐Dimensional van der Waals Materials with Flat Bands

Observation of Electrically Tunable van Hove Singularities in Twisted Bilayer Graphene from NanoARPES

Contact Info

Product

Resources

About