• 文献标题:   Spin and valley ordering of fractional quantum Hall states in monolayer graphene
  • 文献类型:   Article
  • 作  者:   LE ND, JOLICOEUR T
  • 作者关键词:  
  • 出版物名称:   PHYSICAL REVIEW B
  • ISSN:   2469-9950 EI 2469-9969
  • 通讯作者地址:  
  • 被引频次:   1
  • DOI:   10.1103/PhysRevB.105.075203
  • 出版年:   2022

▎ 摘  要

We study spin and valley ordering in the quantum Hall fractions in monolayer graphene at Landau level filling factors nu(G) = -2 n/3 (n = 2, 4, 5). We use exact diagonalizations on the spherical as well as toroidal geometry by taking into account the effect of realistic anisotropies that break the spin/valley symmetry of the pure Coulomb interaction. We also use a variational method based on eigenstates of the fully SU(4) symmetric limit. For all the fractions we study, there are two-component states for which the competing phases are generalizations of those occurring at neutrality nu(G) = 0. They are ferromagnetic, antiferromagnetic, charge-density wave, and Kekule phases, depending on the values of Ising or XY anisotropies in valley space. The varying spin-valley content of the states leads to ground-state quantum numbers that are different from the nu(G) = 0 case. For filling factor nu(G) = -2 + 5/3, there is a parent state in the SU(4) limit that has a flavor content (1, 1/3, 1/3, 0) where the two components that are one-third filled form a two-component singlet. The addition of anisotropies leads to the formation of new states that have no counterpart at nu(G) = 0. While some of them are predicted by the variational approach, we find notably that negative Ising-like valley anisotropy leads to the formation of a state that is a singlet in both spin and valley space and lies beyond the reach of the variational method. Also fully spin polarized two-component states at nu = -2 + 4/3 and -2 + 5/3 display an emergent SU(2) valley symmetry because they do not feel point-contact anisotropies. We discuss implications for current experiments concerning possible spin transitions.