Mirror-symmetry protected topological phase in a zigzag ladder with staggered potential

We study spinless fermions on a zigzag ladder subjected to staggered on-site potential along both of its legs. Three insulating phases, including a charge-density-wave at half-filling, and two dimer insulators at quarter and three-quarter fillings, are identified. The two dimer insulators admit topological phases at opposite signs of the on-site potential, protected by the underlying mirror-symmetry. The phases are characterized by a quantized value of the Zak phase as well as of the entanglement entropy. By performing a projection to the lower and upper two bands separately we show that the system reveals an emergent chiral symmetry. Using density-matrix renormalization group simulations, the topological phases are shown to be remarkably robust against any amount of nearest-neighbor inter-leg as well as intra-leg interactions. Our results are supported by quantum Monte-Carlo simulations in applicable limits of the ladder.