One-dimensional topological metal

TL;DR

This paper introduces a new class of one-dimensional topological metals with protected edge states within gapless bulk states, characterized by a $ ext{Z}$ invariant, and explores their phase diagram, stability, and potential experimental realizations.

Contribution

It presents a novel topological metal phase in 1D superlattices with spin-orbit coupling, protected by symmetries, and analyzes its properties and stability.

Findings

Topological metal phase with edge states within gapless bulk states.

Phase diagram includes gap closing-reopening transitions.

Stability depends on spin rotational symmetry.

Abstract

We propose a new type of topological states of matter exhibiting topologically nontrivial edge states (ESs) within gapless bulk states (GBSs) protected by both spin rotational and reflection symmetries. A model presenting such states is simply comprised of a one-dimensional reflection symmetric superlattice in the presence of spin-orbit coupling containing odd number of sublattices per unit cell. We show that the system has a rich phase diagram including a topological metal (TM) phase where nontrivial ESs coexist with nontrivial GBSs at Fermi level. Topologically distinct phases can be reached through subband gap closing-reopening transition depending on the relative strength of inter and intra unit cell spin-orbit couplings. Moreover, topological class of the system is AI with an integer topological invariant called $\mathbb{Z}$ index. The stability of TM states is also analyzed against Zeeman magnetic fields and on-site potentials resulting in that the spin rotational symmetry around the lattice direction is a key requirement for the appearance of such states. Also, possible experimental realizations are discussed.