Observation of the Josephson plasma mode for a superfluid 3He weak link
Physical Review B American Physical Society (APS) 61:6 (2000) 4196-4199
Imaging the effects of individual zinc impurity atoms on superconductivity in Bi2Sr2CaCu2O8+delta
Nature 403:6771 (2000) 746-750
Abstract:
Although the crystal structures of the copper oxide high-temperature superconductors are complex and diverse, they all contain some crystal planes consisting of only copper and oxygen atoms in a square lattice: superconductivity is believed to originate from strongly interacting electrons in these CuO2 planes. Substituting a single impurity atom for a copper atom strongly perturbs the surrounding electronic environment and can therefore be used to probe high-temperature superconductivity at the atomic scale. This has provided the motivation for several experimental and theoretical studies. Scanning tunnelling microscopy (STM) is an ideal technique for the study of such effects at the atomic scale, as it has been used very successfully to probe individual impurity atoms in several other systems. Here we use STM to investigate the effects of individual zinc impurity atoms in the high-temperature superconductor Bi2Sr2CaCu2O8+delta. We find intense quasiparticle scattering resonances at the Zn sites, coincident with strong suppression of superconductivity within approximately 15 A of the scattering sites. Imaging of the spatial dependence of the quasiparticle density of states in the vicinity of the impurity atoms reveals the long-sought four-fold symmetric quasiparticle 'cloud' aligned with the nodes of the d-wave superconducting gap which is believed to characterize superconductivity in these materials.Bi-state Superfluid H3e Weak Links and the Stability of Josephson π States
Physical Review Letters American Physical Society (APS) 83:19 (1999) 3860-3863
Atomic-scale quasi-particle scattering resonances in Bi2Sr2CaCu2O8+delta
Science (New York, N.Y.) 285:5424 (1999) 88-91
Abstract:
Low-temperature scanning tunneling spectroscopy of the high transition temperature (high-Tc) cuprate Bi2Sr2CaCu2O8+delta reveals the existence of large numbers of identical regions with diameters of about 3 nanometers that have a relatively high density of low-energy quasi-particle states. Their spatial and spectroscopic characteristics are consistent with theories of strong quasi-particle scattering from atomic-scale impurities in a d-wave superconductor. These characteristics include breaking of local particle-hole symmetry, a diameter near twice the superconducting coherence length, and an inverse square dependence of their local density-of-states on distance from the scattering center. In addition to the validation of d-wave quasi-particle scattering theories, these observations identify a source for the anomalously high levels of low-energy quasi-particles in Bi2Sr2CaCu2O8+delta at low temperatures.Search for Superconductivity in Lithium
Journal of Low Temperature Physics Springer Nature 114:5-6 (1999) 445-454