Optical study of Dirac fermions and related phonon anomalies in the antiferromagnetic compound CaFeAsF

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

doi:10.1103/PhysRevB.97.195110

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Journal article

Optical study of Dirac fermions and related phonon anomalies in the antiferromagnetic compound CaFeAsF

Xu, Bing Center for High Pressure Science and Technology Advanced Research, Beijing, China - University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Switzerland
Xiao, H. Center for High Pressure Science and Technology Advanced Research, Beijing, China
Gao, B. Center for High Pressure Science and Technology Advanced Research, Beijing, China
Ma, Y. H. Laboratory of Functional Materials, Chinese Academy of Sciences, Shanghai, China
Mu, G. Laboratory of Functional Materials, Chinese Academy of Sciences, Shanghai, China
Marsik, Premysl University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Switzerland
Sheveleva, Evgeniia University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Switzerland
Lyzwa, Fryderyk University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Switzerland
Dai, Y. M. Center for Superconducting Physics, Nanjing University, China
Lobo, R. P. S. M. LPEM, ESPCI Paris, France - Sorbonne Université, Paris, France
Bernhard, Christian University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Switzerland

08.05.2018

Published in:

Physical Review B. - 2018, vol. 97, no. 19, p. 195110

English 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.

Faculty

Faculté des sciences et de médecine

Department

Département de Physique

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