Evidence of a Normal-State Pseudogap in Bulk Superconducting Tunneling Junctions of YBa2Cu3O7-δ

Abstract

Planar contact tunneling experiments have been performed on bulk superconducting tunneling junctions of YBa₂Cu₃O_7-δ in the temperature range 77 -295K. A clear depression in the conductance curves measured, attributed to the pseudogap, has been observed in temperatures above Tc (approx. 90K determined from dc resistivity measurements) before disappearing at T*=275K. The width of the pseudogap has been quantitatively measured as Dps, ave = 25.6meV from the differential conductance plots. These results agree with the current understanding of the phenomenology and nature of this pseudogap, namely: (I) the pseudogap value is relatively temperature-independent; (2) the superconducting gap and the pseudogap have the same d-wave nature; and (3) the superconducting gap evolves from the pseudogap.