Date of Award
Doctor of Philosophy (PhD)
Kyle P. McElroy
Daniel S. Dessau
The superconducting cuprates represent one of the most intriguing condensed matter systems due to their potential to impact future technologies. As such they have garnered a substantial amount of theoretical and experimental interest over the last 27 years. In spite of this fact, many questions remain unanswered such as the nature of the superconducting pairing mechanism and the origin of the structure of their phase diagram. Spectroscopic Imagining Scanning Tunneling Microscopy (SI-STM) has proven to be an extremely useful probe for studying these materials due to the fact that SI-STM allows for the simultaneous measurement of the real space electronic states with atomic precision and the nature of the momentum K-space states.
In this thesis the design and construction of a 5K SI-STM designed for looking at cleavable surfaces, such as the superconducting cuprates, is presented. The k-space nature of the electronic states on Bi2212, as measured by SI-STM, seems to indicate that there is a portion of the Fermi surface which does not super conduct. However, evidence from other probes is mixed. In this thesis, a framework which explains how these “Fermi Arcs” can arise from experimental effects is presented. Followed by an experiment on Bi2212 that shows how one could mistakenly see this “Fermi Arc” signal by adjusting simple experimental dials.
In addition, in this thesis we present a comprehensive study of Bi2212 samples where Fe has been substituted for Cu in the CuO plane. This study reveals a highly localized bound state, with the density of states showing a large asymmetry favoring the hole side. The density of states can be interpreted within a co-tunneling picture which is only valid if the impurity is coupled to the conduction electrons resulting in a local Kondo-like effect. This is the first time a Kondo-like impurity is observed in a d-wave superconductor. Comparisons to experiments where Kondo impurities are observed in s-wave superconductors are presented as well.
Calleja, Eduardo Manuel, "Uncovering the Nature of Various Scattering Sites, Extended and Magnetic, in Bi2Sr2CaCu2O8+5 Using Atomic Resolved Spectroscopy" (2013). Physics Graduate Theses & Dissertations. 93.