# Topological properties in one-dimensional periodic systems

## TL;DR

This paper challenges the notion that Zak phase and related concepts are true topological invariants in 1D systems, demonstrating their description-dependence and boundary property nature.

## Contribution

It shows that topological properties in 1D periodic systems are description-dependent and not genuine topological invariants, questioning previous classifications.

## Key findings

- Zak phase depends on gauge and unit cell choice
- Edge states can be present or absent depending on boundary definitions
- Localized states are boundary properties, not topological invariants

## Abstract

Recently there is trend to study topological properties in one-dimensional(1D) periodic systems. Concepts such as Zak phase are considered as topological invariants that characterize the bulk bands. The bulk 1D systems are classified to topologically nontrivial and trivial phases according to the value of the so-called topological invariant. The existence of edge states or interface states is viewed as a hallmark of the topological nontriviality of the 1D systems. In this work we demonstrate the so-called topological properties in 1D systems are not topological by showing they are description-dependent: the same system can be both topological and trivial depending on how we describe the system. We demonstrate that Zak phase and other related concepts are not topological invariants by showing they depend on the choice of gauge, especially on the choice of unit cell. We show, for the same bulk system, edge states or interface states can be both present and absent depending the choices of boundaries. So the existence of localized states in 1D system is only a boundary property.