Unveiling three types of fermions in a nodal ring topological semimetal through magneto-optical transitions

TL;DR

This study reveals three distinct fermion types in a nodal ring semimetal SrAs$_3$ through magneto-optical measurements, highlighting the emergence of semi-Dirac fermions at the nodal ring endpoints and their unique quantum properties.

Contribution

The paper identifies and characterizes three types of fermions in a nodal ring semimetal, including the novel semi-Dirac fermions, through combined experimental and theoretical analysis.

Findings

Observation of Landau levels scaling as √B, B^{2/3}, and B.

Identification of Dirac, semi-Dirac, and classical fermions.

Semi-Dirac fermions emerge from nodal ring endpoints.

Abstract

We investigate the quasiparticles of a single nodal ring semimetal SrAs$_3$ through axis-resolved magneto-optical measurements. We observe three types of Landau levels scaling as $\varepsilon \sim \sqrt{B}$, $\varepsilon \sim B^{2/3}$, and $\varepsilon \sim B$ that correspond to Dirac, semi-Dirac, and classical fermions, respectively. Through theoretical analysis, we identify the distinct origins of these three types of fermions present within the nodal ring. In particular, semi-Dirac fermions--a novel type of fermion that can give rise to a range of unique quantum phenomena--emerge from the endpoints of the nodal ring where the energy band disperses linearly along one direction and quadratically along the perpendicular direction, a feature not achievable in nodal point or line structures. The capacity of the nodal ring to simultaneously host multiple fermion types, including semi-Dirac fermions, establishes it as a valuable platform to expand the understanding of topological semimetals.