  Electronic Raman scattering with in and out of (ab) plane polarizations have
been performed on HgBa2Ca2Cu3O8+d in a slightly underdoped single crystal with
a critical temperature Tc=122 K. We find that the d-wave pairing gap at the
antinodes is higher in energy (14 kBTc) than in other cuprates and that it
varies very slowly up to Tc. This hints at a strong coupling nature of the
pairing mechanism. Interestingly, we reveal that the pairing-gap feature in the
Raman response displays a complex peak-dip-hump structure, in a fashion
reminiscent of what observed by angle resolved photo-emission spectroscopy in
Bi2Sr2CaCu2O8+d (Bi-2212). We detect two other distinct superconducting peaks
at 5kBTc and 7kBTc when probing respectively around the nodes and on the whole
Fermi surface. Finally we establish that the pairing gap at the antinodes is
detected both for (ab) plane and for c-axis light polarizations. This shows
that the quasiparticle dynamics along the c-axis is intimately connected to the
antinodal one in the (ab) plane.
