  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 86-78~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(OD80). The differential
conductance above the gap edge shows clear dip structure which is highly
suggestive of strong coupling to a narrow boson mode. Data below the gap edge
suggest that tunnelling is weaker near the nodes of the d-wave gap and give
clear evidence for strong $T$-dependent pair breaking. These findings could
help theorists make a detailed Eliashberg analysis and thereby contribute
towards understanding the pairing mechanism. We show that for our OD80 crystal
the gap above $T_c$ although large, is reasonably consistent with the theory of
superconducting fluctuations.
