Observation of pseudogap in Bi2Sr2CaCu2O8+δ single crystals with electron tunneling spectroscopy

Abstract

We report electron tunneling evidence for a pseudogap in the normal state excitation spectrum of as-grown Bi2Sr2CaCu2O8+δ (Bi2212) single crystals. The normalized conductance curves show that the gap structure does not disappear at Tc but at much higher temperature T∗; the lower bound of T∗ is within 110 K to 150 K for the investigated three junctions. The result gives a support for the existence of paired carriers in the normal state of cuprate superconductor Bi2212.