Two-dimensional Dirac fermions and quantum magnetoresistance in CaMnBi2

Abstract

We report two-dimensional Dirac fermions and quantum magnetoresistance in single crystals of CaMnBi${}_{2}$. The nonzero Berry's phase, small cyclotron resonant mass, and first-principles band structure suggest the existence of the Dirac fermions in 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 ($\ensuremath{\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.