Anomalous Raman scattering from phonons and electrons of superconducting

We report interesting anomalies in the temperature dependent Raman spectra of FeSe0.82 measured from 3 K to 300 K in the spectral range from 60 to 1800 cm−1 and determine their origin using complementary first-principles density functional calculations. A phonon mode near 100 cm−1 exhibits a sharp increase by ∼5% in the frequency below a temperature T s (∼100 K) attributed to strong spin–phonon coupling and onset of short-range antiferromagnetic order. In addition, two high frequency modes are observed at 1350 cm−1 and 1600 cm−1, attributed to electronic Raman scattering from ( x 2 – y 2 ) to x z / y z d-orbitals of Fe.