Fingerprints of spin mediated pairing in cuprates

We demonstrate that the feedback effect from bosonic excitations on fermions, which in the past allowed one to verify the phononic mechanism of a conventional, s-wave superconductivity, may also allow one to experimentally detect the 'fingerprints' of the pairing mechanism in cuprates. We argue that for spin-mediated d-wave superconductivity, the fermionic spectral function, the density of states, the tunneling conductance through an insulating junction, and the optical conductivity are affected by the interaction with collective spin excitations, which below T-c are propagating, magnon-like quasiparticles with gap Delta (s). We show that the interaction with a propagating spin excitation gives rise to singularities at frequencies Delta + Delta (s) for the spectral function and the density of states, and at 2 Delta + Delta (s) for tunneling and optical conductivities, where Delta is the maximum value of the d-wave gap. We further argue that recent optical measurements also allow one to detect subleading singularities at 4 Delta and 2 Delta + 2 Delta (s). We consider the experimental detection of these singularities as a strong evidence in favor of the magnetic scenario for superconductivity in cuprates. (C) 2001 Elsevier Science B.V. All rights reserved.