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Seminars

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  • Title:Novel phases at Van Hove singularities in graphene moiré systems
  • Start Date/Time:2020-12-08 / 13:30
  • End Date/Time :2020-12-08 / 15:10
    • Speaker:Mr. Yu-Ping Lin (University of Colorado Boulder)
    • Place:R019, Phys. Building
    • Host:Prof. Po-Yao Chang (NTHU)
    • Abstract:I will present weak-coupling renormalization group analyses and explain how various novel correlated phases can develop at the Van Hove singularities in graphene moiré systems. Motivated by the structures of low-energy flat bands on the moiré superlattices, I will focus on the two-orbital hexagonal lattice models at the Van Hove doping. First, I will show that a chiral 'high-Tc'-like phase diagram is hosted by an SU(4) symmetric model with conventional Van Hove singularity. Here a d-wave staggered-flux Chern insulator is flanked by the d-wave chiral superconducting domes on both sides of doping. Upon valley splitting which breaks the SU(4) symmetry, the phase diagram turns into a competition between chiral superconductivity and various spin and/or valley density waves. Second, I will demonstrate how various polarized ordered phases may occur when the Van Hove singularities become 'high-order'. These include the p-wave chiral and helical and d-wave chiral superconductivities, s-wave ferromagnetism, as well as f-wave and p-wave polar valley-polarized orders.

      Reference:
      [1] Y.-P. Lin and R. M. Nandkishore, Phys. Rev. B 100, 085136 (2019).
      [2] Y.-P. Lin and R. M. Nandkishore, arXiv:2008.05485.

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