paper

The Hidden Nematic Fluctuations in the Triclinic (Ca0.85La0.15)10(Pt3As8)(Fe2As2)5 Superconductor Revealed by Ultrafast Optical Spectroscopy

arXiv:2305.18763 · doi:10.1103/PhysRevB.108.205136

Abstract

We reported the quasiparticle relaxation dynamics of an optimally doped triclinic iron-based superconductor (Ca $_{0.85}$ La $_{0.15}$ ) $_{10}$ (Pt $_{3}$ As $_{8}$ )(Fe $_{2}$ As $_{2}$ ) $_{5}$ with bulk $T_{c}$ = 30 K using polarized ultrafast optical pump-probe spectroscopy. Our results reveal anisotropic transient reflectivity induced by nematic fluctuations develops below $T_{n e m}$ $\approx$ 120 K and persists in the superconducting states. Measurements under high pump fluence reveal three distinct, coherent phonon modes at frequencies of 1.6, 3.5, and 4.7 THz, corresponding to $A_{1 g} (1)$ , $E_{g}$ , and $A_{1 g} (2)$ modes, respectively. The high-frequency $A_{1 g} (2)$ mode corresponds to the $c$ -axis polarized vibrations of FeAs planes with a nominal electron-phonon coupling constant $I^»_{A_{1 g} (2)}$ $\approx$ 0.139 $\pm$ 0.02. Our findings suggest that the superconductivity and nematic state are compatible but competitive at low temperatures, and the $A_{1 g}$ phonons play an important role in the formation of Cooper pairs in (Ca $_{0.85}$ La $_{0.15}$ ) $_{10}$ (Pt $_{3}$ As $_{8}$ )(Fe $_{2}$ As $_{2}$ ) $_{5}$ .

6 pages, 3 figures and Supplemental Materials