Prof. J. C. Seamus Davis

Abstract:

Scanning tunneling spectroscopy of the high-Tc superconductor Bi2Sr2CaCu2O8+delta reveals weak, incommensurate, spatial modulations in the tunneling conductance. Images of these energy-dependent modulations are Fourier analyzed to yield the dispersion of their wavevectors. Comparison of the dispersions with photoemission spectroscopy data indicates that quasiparticle interference, due to elastic scattering between characteristic regions of momentum-space, provides a consistent explanation for the conductance modulations, without appeal to another order parameter. These results refocus attention on quasiparticle scattering processes as potential explanations for other incommensurate phenomena in the cuprates. The momentum-resolved tunneling spectroscopy demonstrated here also provides a new technique with which to study quasiparticles in correlated materials.

Abstract:

Scanning tunneling spectroscopy measurements of the CuO chain plane in YBa2Cu3O6+xshowing a ≅25 meV gap in the local density of states (LDOS) filled by numerous intragap resonances were presented. Intense peaks in LDOS spectra associated with one dimensional, Friedel-like oscillations were analyzed. The results from other probes as well as their implications for phenomena in the superconducting CuO2plane were also discussed.

Abstract:

We present scanning tunneling spectroscopy measurements of the CuO chain plane in YBa(2)Cu(3)O(6+x), showing an approximately 25 meV gap in the local density of states (LDOS) filled by numerous intragap resonances: intense peaks in LDOS spectra associated with one-dimensional, Friedel-like oscillations. We discuss how these phenomena shed light on recent results from other probes, as well as their implications for phenomena in the superconducting CuO(2) plane.

Abstract:

We have measured mass transport of normal liquid 3He through an array of submicron diameter apertures in a thin membrane. As the temperature is decreased we observe the crossover from viscous flow to ballistic effusion transport by quasiparticles. In this ballistic regime the quasiparticle mean free path is large compared to both the aperture diameter and the membrane thickness, and the flow conductance is temperature independent. At lowest temperatures, this experiment provides an analog of the electronic ballistic point contact for neutral Fermi liquids. The measured conductance is in quantitative agreement with theory.