Xu, Bing Xiao, H. Gao, B. Ma, Y. H. Mu, G. Marsik, Premysl Sheveleva, Evgeniia Lyzwa, Fryderyk Dai, Y. M. Lobo, R. P. S. M. Bernhard, Christian 2018-05-08 We performed optical studies on CaFeAsF single crystals, a parent compound of the 1111-type iron-based superconductors that undergoes a structural phase transition from tetragonal to orthorhombic at Ts=121 K and a magnetic one to a spin density wave (SDW) state at TN=110 K. In the low-temperature optical conductivity spectrum, after the subtraction of a narrow Drude peak, we observe a pronounced singularity around 300cm−1 that separates two regions of quasilinear conductivity. We outline that these characteristic absorption features are signatures of Dirac fermions, similar to what was previously reported for the BaFe2As2 system [Z.-G. Chen et al., Phys. Rev. Lett. 119, 096401 (2017)]. In support of this interpretation, we show that for the latter system this singular feature disappears rapidly upon electron and hole doping, as expected if it arises from a van Hove singularity in between two Dirac cones. Finally, we show that one of the infrared-active phonon modes (the Fe-As mode at 250cm−1) develops a strongly asymmetric line shape in the SDW state and note that this behavior can be explained in terms of a strong coupling with the Dirac fermions. application/pdf https://folia.unifr.ch/global/documents/307175 https://folia.unifr.ch/documents/307175/files/ber_osd.pdf eng info:eu-repo/semantics/altIdentifier/doi/10.1103/PhysRevB.97.195110 info:eu-repo/semantics/openAccess License undefined Physical Review B. - 2018, vol. 97, no. 19, p. 195110 info:eu-repo/classification/udc/53 Optical study of Dirac fermions and related phonon anomalies in the antiferromagnetic compound CaFeAsF http://purl.org/coar/resource_type/c_6501