Publication Highlights

We have developed techniques to double the available energy range for scanning tunneling spectroscopy on fragile surfaces. We employ these techniques on the cuprate high-T_c superconductor Bi_2+ySr_2-yCaCu₂O_8+x to locate the atomic defects which control the local hole concentration, govern the local energy scale of the pseudogap, and pin the periodic charge modulation.

We address several recent claims that the cuprate pseudogap is associated with electronic inversion symmetry breaking. We have implemented a new algorithm for improved spatial resolution scanning tunneling microscopy, which allows us to image a subtle ~5 picometer inversion-symmetry-breaking structural distortion in Bi₂Sr₂Ca_n-1Cu_nO_2n+4+x. Although this structural distortion can impact electronic measurements, we show from its insensitivity to temperature, magnetic field and doping, that it cannot be the long-sought pseudogap state.

VO₂ undergoes an insulator-to-metal transition with up to 5 order of magnitude increase in conductivity near room temperature. We demonstrate controlled local phase switching of a VO₂ film using a biased conducting atomic force microscope tip. Our nanoscale phase manipulation technique opens up the possibility for an understanding of the microscopic mechanism of phase transition in VO₂ as well as its potential relevance to solid state devices.

We provide the first atomic resolution spectroscopy, impurity imaging, and vortex imaging in the new family of Fe-based high-T_c superconductors. We extract the spatial variations of the superconducting gap, the superconducting coherence length, and properties of the vortex pinning.