Quasi-two-dimensional Dirac fermions and quantum magnetoresistance in LaAgBi$_2$

TL;DR

This study uncovers quasi-two-dimensional Dirac fermions in LaAgBi$_2$, demonstrating quantum magnetoresistance behavior linked to the quantum limit of Dirac fermions, highlighting a new class of layered compounds with potential topological properties.

Contribution

It reveals the existence of quasi-2D Dirac fermions in LaAgBi$_2$, a rare-earth layered compound, and characterizes its quantum magnetoresistance behavior, expanding understanding of Dirac materials.

Findings

Identification of Dirac-cone-like points at the Fermi level.

Observation of a crossover from $B^2$ to linear magnetoresistance.

Evidence of quasi-2D Dirac fermions in LaAgBi$_2$.

Abstract

We report quasi-two-dimensional Dirac fermions and quantum magnetoresistance in LaAgBi$_2$. The band structure shows several narrow bands with nearly linear energy dispersion and Dirac-cone-like points at the Fermi level. The quantum oscillation experiments revealed one quasi-two-dimensional Fermi pocket and another complex pocket with small cyclotron resonant mass. The in-plane transverse magnetoresistance exhibits a crossover at a critical field $B^*$ from semiclassical weak-field $B^2$ dependence to the high-field unsaturated linear magnetoresistance which is attributed to the quantum limit of the Dirac fermions. Our results suggest the existence of quasi 2D Dirac fermions in rare-earth based layered compounds with two-dimensional double-sized Bi square nets, similar to (Ca,Sr)MnBi$_{2}$, irrespective of magnetic order.