| This dissertation covers measurements on the high temperature superconductor Bi2Sr2CaCu2O8+delta as performed with a low temperature, ultra high vacuum scanning tunneling microscope (STM). The work involves studying the issue of electronic inhomogeneity on nanometer length scales. The first section contains a brief introduction to BSCCO and some of its properties relevant to STM measurements. Then I discuss the STM itself in terms of principle of operation, construction, and associated measurement electronics.;The next section is of measurements on the nearly 4-lattice-constant periodic modulations in the density of states. These modulations exist in BSCCO both in the form of a charge-ordered state, which may represent new phases, and also as quasi-particle scattering, a band structure effect. To tell these two effects apart, I look at their dispersion (energy vs. wavelength) characteristics, and also the effect they have on the coherence peak heights. I show that the non-dispersive charge ordered state tends to exist most strongly in regions of large gap, which resembles the results of other studies of BSCCO at low dopings. Further analysis suggests that these modulations are fluctuating and have a uni-directional nature.;Finally I will focus on the (non-periodic) nano-scale electronic inhomogeneities seen in this material, namely the spatial variations of the superconducting gap. While it is known that BSCCO has regions of gaps that are smaller or larger than the average, the reason for the excessive heights of the coherence peaks in the small gap regions, or the short peaks in the large gap regions were unknown. I compare experimental data (taken with high spatial and energy resolution) to a numerical model that places a patch of one gap in a sea of another. The results show good qualitative agreement, both in the shapes of the coherence peaks and the spatial evolution of spectra from inside the region to outside. This is followed by analysis involving the energy moments to determine the true gap values.;In the appendix I include my work measuring the charge density wave (CDW) in the quasi-2D material TbTe3. The analysis indicates that the CDW is fully incommensurate with wave-vector qCDW ≈0.71 x 2pi/c. Imaging at various tip-sample voltages highlights effects of the sub-surface layer and its effect on the CDW. An additional (possibly surface) dimerization and ≈ 0.68 x 2pi/alpha ordering perpendicular to the CDW was also observed for the first time. |
