Electronic Raman scattering in Bi-based superconductors under pressure

Determining the nature of interaction responsible for the Cooper-pair formation in cuprates remains unsettled. The most probable candidates are lattice vibrations (phonons) and spin fluctuation modes. Recently, it has been argued that Raman scattering in $B_{1g}$ symmetry may serve as a probe to distinguish between phonon-mediated and magnetically mediated $d$-wave superconductivity. Here we report the results of electronic Raman scattering measurements in Bi-based bilayer and trilayer superconductors at high pressures and at temperatures around 12 K. As a clean and effective tool, pressure enhances $T_{c}$ and thus increases the pairing interaction in these materials. Meanwhile, we find that pressure also brings about the change of the $B_{1g}$ mode. The observed evolution of $B_{1g}$ modes with pressure sheds important insight on the pairing mechanism of high-$T_{c}$ superconductivity.