# Nodal Line Spin-gapless Semimetals and High-quality Candidate Materials

## TL;DR

This paper introduces a new class of topological nodal line spin-gapless semimetals (TNLSGSMs) with protected surface states, proposing specific high-quality materials that could advance spintronics and topological superconductivity.

## Contribution

It proposes and characterizes a novel $ ext{Z}_2$ class of topological nodal line spin-gapless semimetals with protected surface states, and predicts real materials to realize these states.

## Key findings

- Identification of a new $ ext{Z}_2$ class of TNLSGSMs.
- Prediction of high-quality materials with specific space groups.
- Discovery of nearly flat, fully spin-polarized surface states.

## Abstract

Spin-gapless semimetals (SGSMs), which generate 100\% spin polarization, are viewed as promising semi-half-metals in spintronics with high speed and low consumption. We propose and characterize a new $\mathbb{Z_{\mathrm{2}}}$ class of topological nodal line (TNL) in SGSMs. The proposed TNLSGSMs are protected by space-time inversion symmetry or glide mirror symmetry with two-dimensional (2D) fully spin-polarized nearly flat surface states. Based on first-principles calculations and effective model analysis, a series of high-quality materials with $\textit{R}\overline{3}\textit{c}$ and $\textit{R}{3}\textit{c}$ space groups are predicted to realize such TNLSGSMs (chainlike). The 2D fully spin-polarized nearly flat surface states may provide a route to achieving equal spin pairing topological superconductivity as well as topological catalysts.