EFFECT OF SPONTANEOUS DECAY OF SUPERCONDUCTOR QUASI-PARTICLES IN THE TUNNELING DENSITY-OF-STATES

Superconductivity has been successfully described with either the Land au-Ginzburg theory of second order phase transitions or with strong-co upling versions of the original BCS theory for almost fifty years. Rec ent tunnelling and photoemission data on the cuprate oxide superconduc tors may now provide evidence of corrections to the mean field approxi mation. It has been shown by Zasadzinski et al.a[1992] that there is a dip at eV congruent-to 3DELTA0 in the SIS tunneling conductance, whic h is the derivative of the current across a superconductor-insulator-s uperconductor junction with respect to the applied voltage, for a set of cuprate superconductors whose T(c)'s range from 5.5K to 100K. Recen tly L. Coffey and I[Coffey and Coffey 1993] proposed an explanation of this feature in terms of the spontaneous decay of mean field quasipar ticles. We showed that corrections to the mean field approximation for a superconductor lead to different frequency thresholds for spontaneo us quasiparticle decay with different superconductor order parameter s ymmetries. These effects lead to features in the superconductor densit y of states and in the SIS tunneling conductance and provide experimen tal evidence of d-wave symmetry for the superconductor order parameter in the cuprates. I discuss this model and also evidence of quasiparti cle decay in ARPES data on Bi2Sr2CaCu2O8.