Stacking-Induced Symmetry-Protected Topological Phase Transitions

TL;DR

This paper investigates how stacking two gapped 1D subsystems in the BDI class can induce symmetry-protected topological phase transitions, leading to a nontrivial topological phase in the combined system.

Contribution

It introduces a framework for understanding stacking-induced SPT transitions and demonstrates how trivial subsystems can form nontrivial phases through stacking.

Findings

Stacking trivial subsystems can induce nontrivial SPT phases.

The topological invariant of the combined system is a sum of invariants from subsystems and stacking.

A concrete model shows the transition to a zero-field topological superconductor.

Abstract

We study symmetry-protected topological (SPT) phase transitions induced by stacking two gapped one-dimensional subsystems in BDI symmetry class. The topological invariant of the entire system is a sum of three topological invariants: two from each subsystem and an emerging topological invariant from the stacking. We find that any symmetry-preserving stacking of topologically trivial subsystems can drive the entire system into a topologically nontrivial phase. We explain this intriguing SPT phase transitions by conditions set by orbital degrees of freedom and time-reversal symmetry. To exemplify the SPT transition, we provide a concrete model which consists of an atomic chain and a spinful nanowire with spin-orbit interaction and $s$-wave superconducting order. The stacking-induced SPT transition drives this heterostructure into a zero-field topological superconducting phase.