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

Superconductivity has been successfully described with either the Landau-Ginzburg theory of second order phase transitions or with strong-coupling versions of the original BCS theory for almost fifty years. Recent tunnelling and photoemission data on the cuprate oxide superconductors may now provide evidence of corrections to the mean field approximation. 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, which is the derivative of the current across a superconductor-insulator-superconductor junction with respect to the applied voltage, for a set of cuprate superconductors whose T(c)'s range from 5.5K to 100K. Recently L. Coffey and I[Coffey and Coffey 1993] proposed an explanation of this feature in terms of the spontaneous decay of mean field quasiparticles. We showed that corrections to the mean field approximation for a superconductor lead to different frequency thresholds for spontaneous quasiparticle decay with different superconductor order parameter symmetries. These effects lead to features in the superconductor density of states and in the SIS tunneling conductance and provide experimental evidence of d-wave symmetry for the superconductor order parameter in the cuprates. I discuss this model and also evidence of quasiparticle decay in ARPES data on Bi2Sr2CaCu2O8.