Observation of Dirac surface states in the hexagonal PtBi2, a possible origin of the linear magnetoresistance

TL;DR

This study uncovers Dirac surface states in hexagonal PtBi2 using ARPES and DFT, suggesting these states are key to its large linear magnetoresistance, with implications for spintronics applications.

Contribution

First observation of Dirac surface states in hexagonal PtBi2, linking these states to its linear magnetoresistance phenomenon.

Findings

Dirac surface states found at the $ar{ ext{Γ}}$-point crossing the Fermi level.

Surface states exhibit spin polarization as indicated by dichroic measurements.

Surface states likely contribute to the observed linear magnetoresistance.

Abstract

The nonmagnetic compounds showing extremely large magnetoresistance are attracting a great deal of research interests due to their potential applications in the field of spintronics. PtBi$_2$ is one of such interesting compounds showing large linear magnetoresistance (MR) in its both the hexagonal and pyrite crystal structure. We use angle-resolved photoelectron spectroscopy (ARPES) and density functional theory (DFT) calculations to understand the mechanism of liner MR observed in the hexagonal PtBi$_2$. Our results uncover for the first time linear dispersive surface Dirac states at the $\bar{\Gamma}$-point, crossing Fermi level with node at a binding energy of $\approx$ 900 meV, in addition to the previously reported Dirac states at the $\bar{M}$-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 $\bar{\Gamma}$ and $\bar{M}$-points are likely to play a crucial role for the linear field dependent magnetoresistance recorded in this compound.