Multiband effects and the possible Dirac states in LaAgSb$_2$

Abstract

Here we report the possible signature of Dirac fermions in the magnetoresistance, Hall resistivity and magnetothermopower of LaAgSb$_2$. The opposite sign between Hall resistivity and Seebeck coefficient indicates the multiband effect. Electronic structure calculation reveals the existence of the linear bands and the parabolic bands crossing the Fermi level. The large linear magnetoresistance was attributed to the quantum limit of the possible Dirac fermions or the breakdown of weak-field magnetotransport at the charge density wave phase transition. Analysis of Hall resistivity using two-band model reveals that Dirac holes which dominate the electronic transport have much higher mobility and larger density than conventional electrons. Magnetic field suppresses the apparent Hall carrier density, and also induces the sign change of the Seebeck coefficient from negative to positive. These effects are possibly attributed to the magnetic field suppression of the density of states at the Fermi level originating from the quantum limit of the possible Dirac holes.