Interlayer tunnelling evidence for possible electron-boson interactions in $\rm{Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}}$

We report intrinsic tunnelling data for mesa structures fabricated on three over- and optimally-doped $\rm{Bi_{2.15}Sr_{1.85}CaCu_{2}O_{8+\delta}}$ crystals with transition temperatures of 86-80 K and 0.16-0.19 holes per CuO$_2$ unit, for a wide range of temperature ($T$) and applied magnetic field ($H$), primarily focusing on one over-doped crystal. The differential conductance above the gap edge shows clear structure with informative $T$ and $H$ dependence. Data below the gap edge imply that the tunnelling process is mainly coherent and give clear evidence for strong $T$-dependent pair breaking. These findings are important for a detailed analysis in terms of Eliashberg theory and could help to clarify the pairing mechanism.