Superconducting gap excitations in MgB/sub 2/ revealed via time-domain thz spectroscopy

Summary form only given. The surprising discovery of superconductivity in MgB,´ at remarkably high transition-temperatures challenges the limits of phonon-mediated superconductivity, a fundamental question in view of suggested phonon involvement in the high-T, cuprates. Possible anisotropic or unconventional pairing mechanisms have inspired experiments which probe the density of states and superconducting gap, but the large variation of gap values from surface-sensitive and bulk probes seems Optical experiments offer distinct advantages since they penetrate appreciably inside the bulk and simultaneously provide a contactless measure of the candensate within the sampled volume. Here, we present the first measurements of the far-infrared canductivity of MgB, that encompass a frequency range spanning excitations ~ETOSS the fundamental superconducting energy gap.