Nematic response revealed by coherent phonon oscillations in BaFe2As2

Abstract

©2022 American Physical SocietyWe investigate coherent phonon oscillations of BaFe2As2 using optical pump-probe spectroscopy. Time-resolved optical reflectivity shows periodic modulations due to the A1g coherent phonon of c-axis arsenic vibrations. Optical probe beams polarized along the orthorhombic a and b axes reveal that the initial phase of coherent oscillations shows a systematic deviation as a function of temperature, although these oscillations arise from the same c-axis arsenic vibrations. The oscillation phase remains anisotropic even in the tetragonal structure, reflecting a nematic response of BaFe2As2. Our study suggests that investigations on the phase of coherent phonon oscillations in optical reflectivity can offer unique evidence of a nematic order strongly coupled to a lattice instability.