Fig. 2.

(A) Symmetry-dependent Raman spectra of FeSe (SP208 crystal) above $T_S$ = 87 K using 2.33 eV photons. The sharp peaks superimposed on the electronic continuum are due to Raman active optical phonons. Also shown in Inset are the schematics k-space structures of the Raman form factors in different symmetries (blue and red colors indicate positive and negative amplitudes, respectively), and the polarization configurations used to select them. (B) Temperature dependence of the low energy $B_{1g}$ spectra above $T_S$. (C) Evolution of the $B_{1g}$ spectra across $T_S$. The Inset shows the spectra across the superconducting transition at $T_c$ = 8.5 K (SP208). The arrows indicate 2$\mathrm{\Delta }$ superconducting peaks.