Fermionic Symmetry-Protected Topological Phase in a Two-Dimensional Hubbard Model

Understand

We study the two-dimensional (2D) Hubbard model using exact diagonalization for spin-1/2 fermions on the triangular and honeycomb lattices decorated with a single hexagon per site.

• In certain parameter ranges, the Hubbard model maps to a quantum compass model on those lattices.
• On the triangular lattice, the compass model exhibits collinear stripe antiferromagnetism, implying $d$-density wave charge order in the original Hubbard model.
• On the honeycomb lattice, the compass model has a unique, quantum disordered ground state that transforms nontrivially under lattice reflection.