Spin liquids and pseudogap metals in the SU(4) Hubbard model in a moiré superlattice

Journal Article · 12 January 2020 · Physical Review B

DOI: https://doi.org/10.1103/physrevb.101.035122 · OSTI ID:1801879

Zhang, Ya-Hui ^[1]; Mao, Dan  ^[2]

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1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); OSTI
2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

Motivated by the realization of spin-valley Hubbard model on a triangular moiré superlattice in ABC trilayer graphene aligned with hexagon boron nitride (hBN) and possibly also in twisted transition metal dichalcogenide homobilayers, we study possible Mott insulating phases and pseudogap metals based on symmetry constraint and parton mean field theories. First, we show that the Luttinger constraint allows two distinct symmetric and featureless Fermi liquids when there is an intervalley Hund's term breaking SU(4) spin rotation. Especially, there exists a symmetric and featureless “pseudogap metal” with small Fermi surfaces. Then, we suggest to search for such an unconventional metallic state by doping the Mott insulator at $$ν_T$$ = 2 . For this purpose, we study the $$ν_T$$ = 2 Mott insulator using the SO(6) Schwinger boson or Schwinger fermion parton. At the SU(4)-symmetric point, we find two symmetric Z₂ spin liquids. With a large anti-intervalley Hund's term, a featureless Mott insulator is natural. Next, we show that doping the featureless Mott insulator or a Z₂ spin liquid can lead to featureless or orthogonal “pseudogap metal” with small Fermi surfaces proportional to the doping. Besides, we also provide one scenario for the evolution from pseudogap metal to the conventional Fermi liquid through an intermediate exotic “deconfined metal” phase. Finally, we give brief comments on the possibility of U(1) spinon Fermi surface state or $$Z_4$$ spin liquid at $$ν_T$$ = 1 .

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: SC0008739
• OSTI ID: 1801879
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 3 Vol. 101; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English