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

Abstract

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 T s = 121 K and a magnetic one to a spin density wave (SDW) state at T N = 110 K. In the low-temperature optical conductivity spectrum, after the subtraction of a narrow Drude peak, we observe a pronounced singularity around 300 cm (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 250 cm −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.

Scaling of the Fano effect of the in-plane Fe-As phonon and the superconducting critical temperature in Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$

“…In the following we focus on the evolution of the latter. At x = 0, in agreement with previous reports [32,33,51], 1/q has a very small negative value in the paramagnetic state that increases strongly in magnitude below T N (Fig. 1a4).…”

“…Although the bare electron-phonon coupling is commonly believed to be very weak [27], it can be strongly increased by the spin-phonon interaction [28][29][30]. This could possibly explain why a strong enhancement of the Fano effect of the in-plane E u Fe-As mode was observed in the o-AF state of undoped BaFe 2 As 2 [31][32][33]. On the other hand, a sizeable Fano effect was also reported for near optimally doped BKFA without AF order [34,35].…”

Electronic and lattice structure of CaFe1−xCoxAsF probed by x-ray absorption spectroscopy

“…This proposal is of unique importance since it could provide abundant material platforms for the investigation of topological superconductivity. Intriguingly, multiple signatures of topological superconductivity, such as the Majorana bound state and the metallic surface state with Dirac Fermions, have been observed in different types of Fe-based superconductors such as CaFeAsF and Fe(Te,Se) [15][16][17][18][19]. Comparing to the A x Bi 2 Se 3 (A=Cu, Sr, Nb) superconducting topological insulators, the relatively high transition temperature make the Fe-based superconductor a promising platform for studying the Majorana fermions and may further advance research on quantum computing.…”

Revealing the pseudogap in Sr3(Ru0.985Fe0.015)2O7Ban1, Xu2, Li3 et al. 2018Phys. Rev. BSelf Cite0000View full textAdd to dashboardCite

“…Besides, one phonon peak at about 600 cm −1 is distinwhich can not be fit well by the Lorentz model, because of 5 fit the phonon line shape with the Fano model [43][44][45][46][47][48]:…”