Possible origin of linear magnetoresistance: Observation of Dirac surface states in layered PtBi2

The nonmagnetic compounds showing extremely large magnetoresistance are attracting a great deal of research interest due to their potential applications in the field of spintronics. PtBi2 is one of such interesting compounds showing large linear magnetoresistance (MR) in both the hexagonal and pyrite crystal structure. We use angle-resolved photoelectron spectroscopy and density functional theory calculations to understand the mechanism of liner MR observed in the layered PtBi2. Our results uncover linear dispersive surface Dirac states at the Γ¯ point, crossing the Fermi level with a node at a binding energy of ≈900 meV, in addition to the previously reported Dirac states at the M¯ point in the same compound. We further notice from our dichroic measurements that these surface states show an asymmetric spectral intensity when measured with left and right circularly polarized light, hinting at a substantial spin polarization of the bands. Following these observations, we suggest that the linear dispersive Dirac states at the Γ¯ and M¯ points are likely to play a crucial role for the linear field dependent magnetoresistance recorded in this compound.