Evidence for Dirac nodes from quantum oscillations in SrFe2As2.

We present a detailed study of quantum oscillations in the antiferromagnetically ordered pnictide compound SrFe2As2 as the angle between the applied magnetic field and crystalline axes is varied. Our measurements were performed on high-quality single crystals in a superconducting magnet, and in pulsed magnetic fields up to 60 T allowing us to observe orbits from several small Fermi-surface pockets. We extract the cyclotron effective mass m* and frequency F for these orbits and track their values as the field is rotated away from the c axis. While a constant ratio of m*/F is expected for a parabolic band, we observe deviations from this behavior. We conclude that this observation points to orbits derived from a band with Dirac dispersion near the Fermi level. [ABSTRACT FROM AUTHOR]