Cataloging topological phases of N stacked Su-Schrieffer-Heeger chains by a systematic breaking of symmetries

Abstract

Two-dimensional (2D) model of a weak topological insulator with an N stacked Su-Schrieffer-Heeger chain is studied. This study starts with a basic model with all the fundamental symmetries (chiral, time reversal, and particle hole) preserved. Different topological phases are introduced in this model by systematically breaking the system's symmetries. The symmetries are broken by introducing different bonds (hopping terms) in the system. First, the chiral symmetry is broken by introducing hopping within each sublattice or intrasublattice hopping, where the hopping strengths of the sublattices are equal in magnitudes but opposite in sign. Then, following Haldane, the time-reversal (TR) symmetry is broken by replacing the real intrasublattice hopping strengths with imaginary numbers without changing the magnitudes. We find that breaking chiral and TR symmetries are essential for the weak topological insulator to be a Chern insulator. These models exhibit nontrivial topology with the Chern number C=±1. The preservation of the particle-hole (PH) symmetry in the system facilitates an analytical calculation of C, which agrees with the numerically observed topological phase transition in the system. An interesting class of topologically nontrivial systems with C=0 is also observed, where the nontriviality is identified by a quantized and fractional 2D Zak phase. Finally, the PH symmetry is broken in the system by introducing unequal amplitudes of intrasublattice hopping strengths, while the equal intrasublattice hopping strengths ensure the preservation of the inversion symmetry. We investigate the interplay of the PH and the inversion symmetries in the topological phase transition. A discussion on the possible experimental realizations of this model is also presented.