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

TL;DR

This paper systematically explores how breaking fundamental symmetries in stacked SSH chains leads to various topological phases, including Chern insulators and systems with fractional Zak phases, advancing understanding of topological phase transitions.

Contribution

It introduces a comprehensive model that demonstrates how symmetry breaking in stacked SSH chains induces different topological phases, including Chern insulators and systems with fractional Zak phases.

Findings

Breaking chiral and TR symmetries yields Chern insulators with C=±1.

Particle-hole symmetry allows analytical calculation of topological invariants.

Systems with C=0 exhibit fractional Zak phases indicating nontrivial topology.

Abstract

Two-dimensional (2D) model of a weak topological insulator with $N$-stacked Su-Schrieffer-Heeger (SSH) 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 sub-lattice or intra-sub-lattice hopping, where the hopping strengths of the sub-lattices are equal in magnitudes but opposite in sign. Then, following Haldane, the time-reversal (TR) symmetry is broken by replacing the real intra-sub-lattice 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 $C = \pm 1$. 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 non-triviality is identified by quantized and fractional 2D Zak phase. Finally, the PH symmetry is broken in the system by introducing unequal amplitudes of intra-sub-lattice hopping strengths, while the equal intra-sub-lattice hopping strengths ensures 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.