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Evidence for quasiparticle excitations from Dirac-type dispersion in SrFe2As2 in quantum oscillation experiments

The antiferromagnetic parent compounds of the iron pnictide superconductors exhibit unusual magnetic and electronic properties which may play a crucial role in the origin of unconventional pairing in these high temperature superconductors. Recent theoretical work [1] and angle-resolved photoemission spectroscopy measurements [2] suggest that the detection of small Fermi-surface pockets from quantum oscillation experiments in these compounds are associated with a Dirac-type dispersion, in support of a nodal spin density wave state which protects the metallic density of states at the Fermi surface from complete gapping [3]. In this work, we provide a further test of this scenario through quantum oscillation measurements using radio frequency techniques on high quality single crystal samples of SrFe2As2 in pulsed magnetic fields up to 60 T. By tracking the ratio of the quasiparticle effective cyclotron mass to the quantum oscillation frequency as a function of magnetic field angle, we observe a dependence consistent with the Fermisurface topology of a Dirac-type dispersion. We discuss the implications of this result on understanding the metallic state of the iron arsenide parent compounds. References [1] N. Harrison and S. E. Sebastian, Phys. Rev. B 80, 224512 (2009). [2] P. Richard, K. Nakayama, T. Sato, M. Neupane, Y.-M. Xu, J. H. Bowen, G. F. Chen, J. L. Luo, N. L. Wang, X. Dai, Z. Fang, H. Ding, and T. Takahashi, Phys. Rev. Lett. 104, 137001 (2010). [3] Y. Ran, F. Wang, H. Zhai, A. Vishwanath, and D.-H. Lee, Phys. Rev. B 79, 014505 (2009).

pnictide superconductors; Fermi-surface; Dirac-like dispersion

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