Kramers nodal lines and Weyl fermions in SmAlSi

TL;DR

This paper provides experimental evidence for Kramers nodal lines and Weyl fermions in the non-centrosymmetric metal SmAlSi, revealing new topological features linked to its magnetic and electronic properties.

Contribution

It is the first to experimentally identify Kramers nodal lines in a real quantum material, specifically in SmAlSi, using multiple advanced techniques.

Findings

Evidence of Kramers nodal lines in SmAlSi

Observation of Weyl fermions in the paramagnetic phase

Insights into magnetic order and topological properties

Abstract

Kramers nodal lines (KNLs) have recently been proposed theoretically as a special type of Weyl line degeneracy connecting time-reversal invariant momenta. KNLs are robust to spin orbit coupling and are inherent to all non-centrosymmetric achiral crystal structures, leading to unusual spin, magneto-electric, and optical properties. However, their existence in in real quantum materials has not been experimentally established. Here we gather the experimental evidence pointing at the presence of KNLs in SmAlSi, a non-centrosymmetric metal that develops incommensurate spin density wave order at low temperature. Using angle-resolved photoemission spectroscopy, density functional theory calculations, and magneto-transport methods, we provide evidence suggesting the presence of KNLs, together with observing Weyl fermions under the broken inversion symmetry in the paramagnetic phase of SmAlSi. We discuss the nesting possibilities regarding the emergent magnetic orders in SmAlSi. Our results provide a solid basis of experimental observations for exploring correlated topology in SmAlSi.