Chiral SO(4) spin-valley density wave and degenerate topological superconductivity in magic-angle twisted bilayer graphene

Lu, Chen1,2; Zhang, Yongyou2; Zhang, Yu3,4,5; Zhang, Ming2; Liu, Cheng-Cheng2; Wang, Yu1; Gu, Zheng-Cheng6; Chen, Wei-Qiang3,4,5; Yang, Fan2

2022-07-26

10.1103/PhysRevB.106.024518

PHYSICAL REVIEW B   Impact Factor & Quartile

2469-9950

2469-9969

Starting from a realistic extended Hubbard model for a px,y-orbital tight-binding model on the Honeycomb lattice, we perform a thorough investigation of the possible electron instabilities in 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 intervalley spin density wave (SDW) and valley density wave (VDW) as well as that between the intervalley singlet and triplet superconductivities (SCs). The other is the D3 symmetry which leads to the degeneracy among the three symmetry-related wave vectors of the density-wave (DW) orders, originating from the Fermi-surface nesting. The interplay between these 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 meanfield energy minimization for the groundstate energy. At the SU(2)??SU(2) symmetric point, the degenerate intervalley SDW and VDW are mixed into a new state of matter dubbed as the chiral SO(4) spin-valley DW. This state simultaneously hosts three four-component vectorial spin-valley 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 presence of a tiny intervalley exchange interaction with coefficient JH ??? 0??? which breaks the SU(2)??SU(2) symmetry, a pure chiral SDW state is obtained. In the case of JH ??? 0+, although a nematic VDW order is favored, the two SDW orders with equal amplitudes are accompanied simultaneously. This nematic VDW+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 JH = 0 near the VH dopings, the former (latter) is favored for JH ??? 0??? (JH ??? 0+). In addition, the two asymmetric dopingdependent behaviors of the obtained pairing phase diagram are well consistent with experiments.

SCI

English

NI Journal Papers

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National Natural Science Foundation of China["12074031","12074037","11922401","11874292","11729402","11574238","11861161001","12141402"] ; Hong Kong's Research Grants Council["N-CUHK427/18","14302021"] ; Science, Technology and Innovation Commission of Shenzhen Municipality[ZDSYS20190902092905285] ; Guangdong Basic and Applied Basic Research Foundation[2020B1515120100] ; Shenzhen-Hong Kong Cooperation Zone for Technology and Innovation[HZQB-KCZYB-2020050]

Materials Science ; Physics

Materials Science, Multidisciplinary ; Physics, Applied ; Physics, Condensed Matter

WOS:000836005100004

AMER PHYSICAL SOC

PHYSICS

Web of Science

1.Wuhan Univ, Sch Phys & Technol, Wuhan 430072, Peoples R China
2.Beijing Inst Technol, Sch Phys, Beijing 100081, Peoples R China
3.Southern Univ Sci & Technol, Shenzhen Key Lab Adv Quantum Funct Mat & Devices, Shenzhen 518055, Peoples R China
4.Southern Univ Sci & Technol, Dept Phys, Shenzhen 518055, Peoples R China
5.Southern Univ Sci & Technol, Inst Quantum Sci & Engn, Shenzhen 518055, Peoples R China
6.Chinese Univ Hong Kong, Dept Phys, Shatin, Hong Kong, Peoples R China

Lu, Chen,Zhang, Yongyou,Zhang, Yu,et al. Chiral SO(4) spin-valley density wave and degenerate topological superconductivity in magic-angle twisted bilayer graphene[J]. PHYSICAL REVIEW B,2022,106(2).

Lu, Chen.,Zhang, Yongyou.,Zhang, Yu.,Zhang, Ming.,Liu, Cheng-Cheng.,...&Yang, Fan.(2022).Chiral SO(4) spin-valley density wave and degenerate topological superconductivity in magic-angle twisted bilayer graphene.PHYSICAL REVIEW B,106(2).

Lu, Chen,et al."Chiral SO(4) spin-valley density wave and degenerate topological superconductivity in magic-angle twisted bilayer graphene".PHYSICAL REVIEW B 106.2(2022).