Kramers Nodal Line Metals

TL;DR

This paper introduces Kramers nodal line metals (KNLMs), a new class of topological materials with doubly degenerate lines connecting time-reversal invariant momenta, expanding the understanding of non-centrosymmetric metals with spin-orbit coupling.

Contribution

It demonstrates that all achiral non-centrosymmetric materials with SOC can be classified as KNLMs, revealing a new topological phase and linking them to Kramers Weyl semimetals.

Findings

Identification of Kramers nodal lines connecting TRIM points.

Classification of Fermi surfaces as spindle torus and octdong types.

Electrons on octdong Fermi surfaces described by 2D massless Dirac Hamiltonians.

Abstract

Recently, it was pointed out that all chiral crystals with spin-orbit coupling (SOC) can be Kramers Weyl semimetals (KWSs) which possess Weyl points pinned at time-reversal invariant momenta. In this work, we show that all achiral non-centrosymmetric materials with SOC can be a new class of topological materials, which we term Kramers nodal line metals (KNLMs). In KNLMs, there are doubly degenerate lines, which we call Kramers nodal lines (KNLs), connecting time-reversal invariant momenta. The KNLs create two types of Fermi surfaces, namely, the spindle torus type and the octdong type. Interestingly, all the electrons on octdong Fermi surfaces are described by two-dimensional massless Dirac Hamiltonians. These materials support quantized optical conductance in thin films. We further show that KNLMs can be regarded as parent states of KWSs. Therefore, we conclude that all non-centrosymmetric metals with SOC are topological, as they can be either KWSs or KNLMs.