Imaging the two gaps of the high temperature superconductor Pb-Bi₂Sr₂CuO₆₊x

Abstract

The nature and behavior of electronic states in high temperature superconductors are the center of much debate. The pseudogap state, observed above the superconducting transition temperature Tc, is seen by some as a precursor to the superconducting state. Others view it as a competing phase. Recently, this discussion has focused on the number of energy gaps in the system. Some experiments indicate a single energy gap, implying that the pseudogap is a precursor state. Others indicate two, suggesting that it is a competing or coexisting phase. In this thesis, I report temperature dependent scanning tunneling spectroscopy of Pb-Bi2Sr2 CuO6+6 . I have developed a novel analytical method that reveals a new, narrow, homogeneous gap that vanishes near Tc, superimposed on the typically observed, inhomogeneous, broad gap, which is only weakly temperature dependent. These results not only support the two gap picture, but also explain previously troubling differences between scanning tunneling microscopy and other experimental measurements.