Midgap states induced by Zeeman field and $p$ wave superconductor pairing

TL;DR

This paper introduces a new topological phase called obstructed superconductor in a spinful SSH-like model with Zeeman field and p-wave pairing, revealing nonchiral midgap states and unique transport properties.

Contribution

It proposes a novel mechanism to realize a spinful SSH model with intrinsic spin-orbit coupling and Zeeman field, and predicts the obstructed superconductor phase with distinctive edge states.

Findings

Identification of midgap states from hidden polarization.

Design of charge pumping via polarization tuning.

Prediction of nonchiral midgap states causing nonlocal conductance.

Abstract

The one-dimensional Su-Schrieffer-Heeger (SSH) model is central to band topology in condensed matter physics, which allows us to understand and design distinct topological states. In this work, we find another mechanism to analogize the SSH model in a spinful system, realizing an obstructed atomic insulator by introducing intrinsic spin-orbit coupling and in-plane Zeeman field. In our model, the midgap states originate from a quantized hidden polarization with invariant index $\mathbb{Z}_2$ (0; 01) due to the local inversion symmetry breaking. When the global inversion symmetry is broken, a charge pumping is designed by tuning the polarization. Moreover, by introducing the $p+ip$ superconductor pairing potential, a new topological phase dubbed obstructed superconductor (OSC) is identified. This new state is characterized by invariant index $\mathbb{Z}_2$ (0; 01) and nonchiral midgap states. More interestingly, these nonchiral edge states result in a chiral-like nonlocal conductance, which is different from the traditional chiral topological superconductor. Our findings not only find another strategy to achieve a spinful SSH model but also predict the existence of OSC, providing a promising avenue for further exploration of its transport properties.