Two dimensional Dirac fermions and quantum magnetoresistance in CaMnBi$_2$

TL;DR

This study identifies two-dimensional Dirac fermions in CaMnBi$_2$ through magnetoresistance measurements and band structure analysis, revealing quantum effects and a crossover from semiclassical to quantum regimes.

Contribution

First demonstration of 2D Dirac fermions in CaMnBi$_2$ via combined experimental and theoretical approaches.

Findings

Observation of quantum magnetoresistance with linear high-field behavior

Detection of non-zero Berry's phase indicating Dirac fermions

Temperature dependence of critical field B* supports linear dispersion splitting

Abstract

We report two dimensional Dirac fermions and quantum magnetoresistance in single crystals of CaMnBi$_2$. The non-zero Berry's phase, small cyclotron resonant mass and first-principle band structure suggest the existence of the Dirac fermions in the Bi square nets. 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 ($\sim 120%$ in 9 T at 2 K) due to the quantum limit of the Dirac fermions. The temperature dependence of $B^*$ satisfies quadratic behavior, which is attributed to the splitting of linear energy dispersion in high field. Our results demonstrate the existence of two dimensional Dirac fermions in CaMnBi$_2$ with Bi square nets.