Evolution of a bosonic mode across the superconducting dome in the   high-Tc cuprate Pr(2-x)Ce(x)CuO(4-{\delta})
  We report a detailed spectroscopic study of the electron doped cuprate superconductor Pr(2-x)Ce(x)CuO(4-{\delta}) using point contact junctions for x=0.125(underdoped), x=0.15(optimally doped) and x=0.17(overdoped). From our conductance measurements we are able to identify bosonic resonances for each doping. These excitations disappear above the critical temperature, and above the critical magnetic field. We find that the energy of the bosonic excitations decreases with doping, which excludes lattice vibrations as the paring glue. We conclude that the bosonic mediator for these cuprates is more likely to be spin excitations. 
Itay Diamant, Shay Hacohen-Gourgy, and Yoram Dagan
cond-mat.supr-con