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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 observed for one orbit as expected for a parabolic band, a clear deviation is observed for another. We conclude that this deviation points to an orbit derived from a band with Dirac dispersion near the Fermi level.

pnictide compound SrFe2As2; quantum oscillations; Dirac Nodes

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