Two-dimensional Massless Dirac Fermions in Antiferromagnetic AFe2As2 (A = Ba, Sr)

Abstract

We report infrared studies of AFe${}_2$As${}_2$ (A = Ba, Sr), two representative parent compounds of iron-arsenide superconductors, at magnetic fields (B) up to 17.5 T. Optical transitions between Landau levels (LLs) were observed in the antiferromagnetic states of these two parent compounds. Our observation of a $\sqrt{B}$ dependence of the LL transition energies, the zero-energy intercepts at B = 0 T under the linear extrapolations of the transition energies and the energy ratio ($\sim$ 2.4) between the observed LL transitions, combined with the linear band dispersions in two-dimensional (2D) momentum space obtained by theoretical calculations, demonstrates the existence of massless Dirac fermions in antiferromagnetic BaFe${}_2$As${}_2$. More importantly, the observed dominance of the zeroth-LL-related absorption features and the calculated bands with extremely weak dispersions along the momentum direction $k_z$ indicate that massless Dirac fermions in BaFe${}_2$As${}_2$ are 2D. Furthermore, we find that the total substitution of the barium atoms in BaFe${}_2$As${}_2$ by strontium atoms not only maintains 2D massless Dirac fermions in this system, but also enhances their Fermi velocity, which supports that the Dirac points in iron-arsenide parent compounds are topologically protected.

arXiv commentMagneto-infrared study, Landau level spectroscopy, DFT+DMFT calculations

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• Two-dimensional Massless Dirac Fermions in Antiferromagnetic AFe2As2 (A = Ba, Sr)
• Fermi surface with Dirac fermions in CaFeAsF determined via quantum oscillation measurements
• Thermoelectric anisotropy in Ba(Fe1-xCox)2As2 iron-based superconductor
• Correlation Driven Phonon Anomalies in Bulk FeSe
• Optical study of Dirac fermions and related phonon anomalies in antiferromagnetic compound CaFeAsF
• Anisotropy of the Seebeck and Nernst coefficients in parent compounds of the iron-based superconductors
• Charge-density wave transition in magnetic topological semimetal EuAl${}_4$
• Thermoelectric signature of the nematic phase in iron-based superconductor
• Layered Topological Antiferromagnetic Metal at Room Temperature -- YbMn${}_2$Ge${}_2$
• Two-dimensional Dirac semimetals with tunable edge states
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• Linear scaling relation between two-dimensional massless Dirac fermion Fermi velocity and Fe-As bond length in iron arsenide superconductor systems
• Observation of the Dirac Dispersions in Co-doped CaFe2As2