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

Ya-Hui Zhang and Dan Mao
Phys. Rev. B 101, 035122 – Published 13 January 2020

Abstract

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 νT=2. For this purpose, we study the νT=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. Last, we give brief comments on the possibility of U(1) spinon Fermi surface state or Z4 spin liquid at νT=1.

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  • Received 9 July 2019
  • Revised 4 November 2019

DOI:https://doi.org/10.1103/PhysRevB.101.035122

©2020 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Ya-Hui Zhang and Dan Mao

  • Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

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Issue

Vol. 101, Iss. 3 — 15 January 2020

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