We report two-dimensional quantum transport in SrMnBi${}_2$ single crystals. The linear energy dispersion leads to unusual nonsaturated linear magnetoresistance since all Dirac fermions occupy the lowest Landau level in the quantum limit. The transverse magnetoresistance exhibits a crossover at a critical field $B^{*}$ from semiclassical weak-field $B^2$ dependence to the high-field linear-field dependence. With an increase in temperature, the critical field $B^{*}$ increases and the temperature dependence of $B^{*}$ satisfies the quadratic behavior which is attributed to the Landau-level splitting of the linear energy dispersion. The effective magnetoresistant mobility ${\mu }_{\text{MR}}\sim 3400$ cm${}^2$/V s is derived. Angular-dependent magnetoresistance and quantum oscillations suggest dominant two-dimensional (2D) Fermi surfaces. Our results illustrate the dominant 2D Dirac fermion states in SrMnBi${}_2$ and imply that bulk crystals with Bi square nets can be used to study low-dimensional electronic transport commonly found in 2D materials such as graphene.

• Received 3 August 2011

DOI:https://doi.org/10.1103/PhysRevB.84.220401