Raman scattering investigation of the electron-phonon coupling in superconducting Nd(O,F)BiS$_2$

We have performed polarized Raman scattering measurements on the newly discovered superconductor Nd(O,F)BiS$_2$ ($T_c = 4$ K). We observe 2 Raman active modes, with frequencies in accordance with first-principles calculations. One A$_{1g}$ phonon mode at 112.4 cm$^{-1}$ exhibits a Fano line shape due to electron-phonon coupling. We find a resonance for this mode at 2.45 eV excitation energy. We estimate a 0.68 contribution of this mode to the electron-phonon coupling constant $λ$. Our Raman results suggest that the BiS$_2$-based superconductors are possibly phonon-mediated BCS superconductors.

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