Center for Functional Nanomaterials Seminar

Scanning tunneling spectroscopy (STS) is a powerful probe of the local (~nm) properties of strongly correlated materials such as the high-temperature superconducting cuprates. For these compounds, STS can provide important coherence-length scale information on the phase and amplitude of the superconducting order parameter (OP). By understanding how the OP evolves as a function of doping, applied field etc., important insight can be obtained on the microscopic mechanism behind high-temperature superconductivity. In this talk I will present a series of STS experiments on thin films of the high-Tc cuprate YBa2Cu3O7 (YBCO).

We have developed a novel technique that combines STS with pulsed spin-polarized quasiparticle injection to examine how the OP evolves under spin disequilibrium. I will discuss this technique and present results on optimally-doped YBCO. I will also present a doping dependent STS study of c-axis YBCO thin films. The c-axis spectrum exhibits multiple spectral features which scale similarly in energy with respect to doping. The multiple features suggest that superconductivity in YBCO may involve both the plane and chain layers. Lastly, I will discuss a recent STS study on the evolution of the d-wave Andreev surface states in an applied magnetic field. Preliminary results will be presented, including a discussion on possible time-reversal symmetry breaking states at the surface of the YBCO.