Quasi-nodal lines in rhombohedral magnetic materials

TL;DR

This paper investigates quasi-nodal lines in magnetic materials where magnetization breaks glide reflection symmetry, leading to small energy gap lines that influence charge and spin transport, especially in half-metallic ferromagnets.

Contribution

It introduces the concept of quasi-nodal lines in magnetic materials and demonstrates their existence in specific trifluorides and trioxides, linking them to transport phenomena.

Findings

Quasi-nodal lines exist in certain magnetic trifluorides and trioxides.

Presence of quasi-nodal lines near the Fermi level affects charge and spin transport.

Large anomalous Hall signals are attributed to quasi-nodal lines in specific ferromagnetic phases.

Abstract

A well-established result in condensed matter physics states that materials crystallizing in symmetry groups containing glide reflection symmetries possess nodal lines on the energy bands. These nodal lines are topologically protected and appear on the fixed planes of the reflection in reciprocal space. In the presence of inversion symmetry, the energy bands are degenerate and the nodal lines on the fixed plane may hybridize or may cross. In the former case, the crossing is avoided, thus producing lines on reciprocal space where the energy gap is small, and in the latter, the nodal lines will endure, thus producing Dirac or double nodal lines. In addition, if the material crystallizes in a ferromagnetic phase where the glide reflection symmetry is broken, the nodal lines hybridize, thus defining lines in reciprocal space where the energy gap is small. In this work we concentrate our efforts on the study of nodal lines that hybridize due to magnetization; we have coined the term of quasi-nodal lines for those lines in reciprocal space where the energy gap is small (less than what can be detected experimentally). We study magnetic trifluorides and trioxides which crystallize in magnetic space groups 167.107 and 161.71 and we show the existence of quasi-nodal lines on these materials. We furthermore show that whenever the quasi-nodal lines are located around the Fermi level then interesting charge and spin transport effects are induced and can be used to detect experimentally these lines. Of particular interest are the half-metallic ferromagnetic phases of PdF3 and LiCuF3 where the large signal of the anomalous Hall conductance is due to the presence of the quasi-nodal lines on the Fermi level.