Superconductivity and phonon self-energy effects in Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$

Abstract

We study Fe1+yTe0.6Se0.4 multi-band superconductor with Tc = 14 K by polarization-resolved Raman spectroscopy. Deep in the superconducting state, we detect pair-breaking excitation at 45 cm −1 (2∆ = 5.6 meV) in the XY (B2g) scattering geometry, consistent with twice of the superconducting gap energy (3 meV) revealed by ARPES on the hole-like Fermi pocket with dxz/dyz character. We analyze the superconductivity induced phonon self-energy effects for the B1g(Fe) phonon and estimate the electron-phonon coupling constant λ Γ ≈ 0.026, which is insufficient to explain superconductivity with Tc = 14 K.