Variable Temperature Scanning Tunneling Microscopy Study of a High Temperature Superconductor Bi2Sr2CaCu2O8+d

We have used a custom-built scanning tunneling microscope (STM) to investigate the electronic states of a slightly underdoped high-TC superconductor Bi2Sr2CaCu2O8+d as a function of temperature. We have demonstrated for the first time that atomicallyresolved spectroscopic studies at elevated temperatures are possible. We have used this new experimental capability to map out electronic states as a function of energy and position at 40 K and 100 K. Atomically resolved spectroscopic mapping combined with the analysis capabilities of Fourier-transform STM allow us to characterize electronic states both in real and reciprocal space. These techniques allow us to analyze our data in the context of many theoretical and experimental results and approaches. Our results confirm many aspects of prior observations at low temperatures. Specifically, our data at 40 K corroborates the identification and characterization of impurity resonances at Zn and Ni sites, and the existence of dispersing modulations of local electronic density of states below the superconducting gap energy. In this thesis, I also present our observations and analysis of the few differences between our data at 40 K and preexisting low-temperature results. The key results at 100 K are our observation of local electronic ordering below the pseudogap energy scale and our failure to observe any tell-tale signs of local superconductivity at Ni impurity sites in the pseudogap regime of a high-TC superconductor. The observation of electronic ordering in the pseudogap regime is a novel and indeed a highly unexpected result. The existence of such a phenomenon is likely to have substantial impact on our understanding of the pseudogap regime. Our tunneling spectroscopy observations at the Ni sites reveal a clear difference between the electronic states above and below TC. This is a novel result in its own right. It unambiguously shows that single electron spectroscopy can observe sharp differences between the various cuprate phases. This observation makes STM a valuable tool and holds the promise of using it to map out electronic states and phases across the entire phase diagram.U of I OnlyStudent has not yet granted open access permissio