Topological Order and Symmetry-Protected Topological Phase: Spin Liquids on Kagome and Honeycomb Lattices

  • Event Date: 2016-07-27
  • AMO/QIS/CMT
  • Speaker: Prof. Cheng-Chien Chen (陳正乾) (Department of Physics, University of Alabama at Birmingham, USA)  /  Host: Prof. Chung-Yu Mou (NTHU)
    Place: P512 of NCTS, 5F, 3rd General Building, Nat'l Tsing Hua Univ.

Landau theory of symmetry breaking provides a universal understanding for transition between phases of different order parameters. However, there are states of matter containing “topological order” which is beyond the usual symmetry description. Here I will first discuss the spin-1/2 kagome Heisenberg model with further-neighbor exchange and Dzyaloshinskii-Moriya interaction [1]. Its phase diagram exhibits rich behaviors ranging from long-range magnetism to topological spin liquid. I will next discuss a Hubbard model with spin-1/2 fermions on a decorated honeycomb lattice [2]. Its low-energy effective Hamiltonian is a compass model showing a unique, magnetically disordered ground state that transforms nontrivially under lattice reflection. The corresponding ground state of the Hubbard model is thus a two-dimensional fermionic symmetry-protected topological phase and cannot be connected adiabatically to a free-fermion topological state.
 
References:
[1] T. F. Seman et al., arXiv:1508.01523.
[2] C.-C. Chen et al., arXiv:1603.03439.
 

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