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$_{2}$

B. Xu; E. Cappelluti; L. Benfatto; B. P. P. Mallett; P. Marsik; E. Sheveleva; F. Lyzwa; Th. Wolf; R. Yang; X. G. Qiu; Y. M. Dai; H. H. Wen; R. P. S. M. Lobo; C. Bernhard

doi:10.1103/PhysRevLett.122.217002

paper

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 $_{2}$

arXiv:1810.10230 · doi:10.1103/PhysRevLett.122.217002

Abstract

By means of infrared spectroscopy we determine the temperature-doping phase diagram of the Fano effect for the in-plane Fe-As stretching mode in Ba $_{1 - x}$ K $_{x}$ Fe $_{2}$ As $_{2}$ . The Fano parameter $1/ q^{2}$ , which is a measure of the phonon coupling to the electronic particle-hole continuum, shows a remarkable sensitivity to the magnetic/structural orderings at low temperatures. More strikingly, at elevated temperatures in the paramagnetic/tetragonal state we find a linear correlation between $1/ q^{2}$ and the superconducting critical temperature $T_{c}$ . Based on theoretical calculations and symmetry considerations, we identify the relevant interband transitions that are coupled to the Fe-As mode. In particular, we show that a sizable $x y$ orbital component at the Fermi level is fundamental for the Fano effect and possibly also for the superconducting pairing.

Supplemental materials are available upon request

Scaling of the Fano effect of the in-plane Fe-As phonon and the superconducting critical temperature in Ba1−x​Kx​Fe2​As2​

Abstract

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 $_{2}$