Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 10 of 10
Full-Text Articles in Physics
Josephson Scanning Tunneling Microscopy: A Local And Direct Probe Of The Superconducting Order Parameter, Richard P. Barber Jr., Hikari Kimura, Shuhei Ono, Yoichi Ando, Robert C. Dynes
Josephson Scanning Tunneling Microscopy: A Local And Direct Probe Of The Superconducting Order Parameter, Richard P. Barber Jr., Hikari Kimura, Shuhei Ono, Yoichi Ando, Robert C. Dynes
Physics
Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi2Sr2CaCu2O8+ BSCCO samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a scanning tunneling microscope STM equipped with a superconducting tip. The spatial resolution of the STM of lateral distances less than the superconducting coherence length allows it to reveal local inhomogeneities in the pair wave function of the BSCCO. Instrument performance is demonstrated first with Josephson measurements of Pb films followed by the layered superconductor NbSe2. The relevant measurement parameter, the Josephson ICRN product, is discussed within the context of both BCS superconductors …
Scanning Josephson Tunneling Microscopy Of Single Crystal Bi2Sr2Cacu2O8+Δ With A Conventional Superconducting Tip, Richard P. Barber Jr., Hikari Kimura, Shuhei Ono, Yoichi Ando, Robert C. Dynes
Scanning Josephson Tunneling Microscopy Of Single Crystal Bi2Sr2Cacu2O8+Δ With A Conventional Superconducting Tip, Richard P. Barber Jr., Hikari Kimura, Shuhei Ono, Yoichi Ando, Robert C. Dynes
Physics
We have performed both Josephson and quasiparticle tunneling in vacuum tunnel junctions formed between a conventional superconducting scanning tunneling microscope tip and overdoped Bi2Sr2CaCu2O8+δ single crystals. A Josephson current is observed with a peak centered at a small finite voltage due to the thermal-fluctuation-dominated superconducting phase dynamics. Josephson measurements at different surface locations yield local values for the Josephson IcRn product. Corresponding energy gap measurements were also performed and a surprising inverse correlation was observed between the local IcRn product and the local energy gap.
Negative Magnetoresistance, Negative Electroresistance, And Metallic Behavior On The Insulating Side Of The Two-Dimensional Superconductor-Insulator Transition In Granular Pb Films, Richard P. Barber Jr., Shih-Ying Hsu, James M. Valles Jr., Robert C. Dynes, Rolfe Eldridge Glover Iii
Negative Magnetoresistance, Negative Electroresistance, And Metallic Behavior On The Insulating Side Of The Two-Dimensional Superconductor-Insulator Transition In Granular Pb Films, Richard P. Barber Jr., Shih-Ying Hsu, James M. Valles Jr., Robert C. Dynes, Rolfe Eldridge Glover Iii
Physics
Granular Pb thin films on the insulating side of the two-dimensional superconductor-insulator transition are observed to exhibit a large negative magnetoresistance and electroresistance change in resistance with electric field at low temperatures. At high measurement voltages and low temperatures, the film resistances become temperature independent creating a "metallic" state. These phenomena are explained as manifestations of transport due to intergranular quasiparticle tunneling. This explanation might also provide insights into the similar behavior observed in other superconductors.
Resistive Transitions In Quench-Condensed Bi Films Near A Normal-Metal Ground Plane, Richard P. Barber Jr., Ben Kain
Resistive Transitions In Quench-Condensed Bi Films Near A Normal-Metal Ground Plane, Richard P. Barber Jr., Ben Kain
Physics
We report observations of the zero-field resistive transitions of superconducting quench-condensed Bi0.97Tl0.03 films both near electrically isolated normal-metal ground planes and on clean fire-polished glass. Transition temperatures, obtained by fitting the data with the two-dimensional Aslamazov-Larkin theory of fluctuation conductance, were found to be significantly enhanced for films deposited over ground planes versus those deposited onto insulating substrates. Conductivity enhancement due to superconducting fluctuations was found to be much less than expected for the thinnest samples. This suppression was coincident with broadened superconductor transitions that are consistent with nonuniform sample thickness. Sufficiently thick films showed reasonable agreement with both the …
Tuning The Transition Temperature Of Superconducting Ag/Pb Films Via The Proximity Effect, Richard P. Barber Jr., Ben Kain, S. R. Khan
Tuning The Transition Temperature Of Superconducting Ag/Pb Films Via The Proximity Effect, Richard P. Barber Jr., Ben Kain, S. R. Khan
Physics
We report measurements of the transition temperature (TC) of superconducting films composed of various combinations of Ag and Pb layers. For samples with good electrical contact between the layers, the measured TC values show reasonable agreement with the Cooper model of the proximity effect. In poorly coupled samples, the normal layers appear to cause little if any suppression of the TC. We present a simple predictive expression for TC as a function of Ag content.
Crossover From Phase Fluctuation To Amplitude-Dominated Superconductivity: A Model System, Richard P. Barber Jr., L. Merchant, J. Ostrick, Robert C. Dynes
Crossover From Phase Fluctuation To Amplitude-Dominated Superconductivity: A Model System, Richard P. Barber Jr., L. Merchant, J. Ostrick, Robert C. Dynes
Physics
We have experimentally studied a model system that demonstrates the crossover from a superconductor that is dominated by phase fluctuations, to one in which the amplitude of the order parameter is the controlling influence on Tc. This model system is comprised of two-dimensional granular Pb with an overlayer of Ag. The system displays many aspects of the phase diagram of the concentration dependence of Tc in the high-Tc superconductors, and this crossover has been applied to explain the phase diagram in that case. We point out the similarities and differences between the model system presented in this paper and the …
Superconductor-Insulator Transition In Granular Pb Films Near A Superconducting Ground Plane, Richard P. Barber Jr., S. R. Khan, Eric Morre Pedersen, Ben Kain, A. J. Jordan
Superconductor-Insulator Transition In Granular Pb Films Near A Superconducting Ground Plane, Richard P. Barber Jr., S. R. Khan, Eric Morre Pedersen, Ben Kain, A. J. Jordan
Physics
We report observations of the zero-field superconductor-insulator transition in granular quench-condensed Pb for samples within 10-15 nm of relatively thick superconducting ground planes. Resistance vs temperature measurements of sufficiently thick Pb samples exhibit broadened superconductor transitions consistent with previous results on clean dielectric substrates. The lack of any measurable influence by the superconducting planes on the Pb film resistance is discussed within the context of zero-field vortex-antivortex unbinding explanations for the transition broadening.
Tunneling Into Granular Pb Films In The Superconducting And Insulating Regimes, Richard P. Barber Jr., L. Merchant, Porta Arthur La, Robert C. Dynes
Tunneling Into Granular Pb Films In The Superconducting And Insulating Regimes, Richard P. Barber Jr., L. Merchant, Porta Arthur La, Robert C. Dynes
Physics
Tunneling measurements have been performed on both sides of the insulator-superconductor transition in quench-condensed granular Pb films. The results indicate that the Pb film consists of fully superconducting grains with essentially bulk values for the superconducting energy gap and transition temperature, even when the film exhibits insulating behavior in transport measurements. The density of states inferred from measurements in perpendicular magnetic field are consistent with magnetic spin-flip broadening.
Low-Field Magnetoresistance In Granular Pb Films Near The Insulator-Superconductor Transition, Richard P. Barber Jr., Robert C. Dynes
Low-Field Magnetoresistance In Granular Pb Films Near The Insulator-Superconductor Transition, Richard P. Barber Jr., Robert C. Dynes
Physics
We have studied the insulator-superconductor transition in quench-condensed granular Pb films from 0.1 to 10 K. Resistance measurements were made in zero magnetic field and low noise conditions. Magnetoresistance measurements were also performed for low magnetic fields (less than 100 G). The magnetoresistance results on the superconducting side of the transition suggest that we are directly probing the finite length scales associated with the range of phase coherence in these granular materials.
Hyper-Resistivity To Global-Superconductivity Transition By Annealing In Quench-Condensed Pb Films, Richard P. Barber Jr., Rolfe Eldridge Glover Iii
Hyper-Resistivity To Global-Superconductivity Transition By Annealing In Quench-Condensed Pb Films, Richard P. Barber Jr., Rolfe Eldridge Glover Iii
Physics
The rapid rise in resistance occurring in barely conducting quench-condensed Pb films cooled through temperatures characteristic of the bulk superconducting transition is found to be strongly current dependent, the resistance increasing rapidly with decreasing current and temperature. Annealing the same film at temperatures below 40 K changes the behavior to that of a conventional superconductor with resistance that drops as the film current and temperature decrease. Experimental evidence suggests this results from a transition from quasiparticle-dominated to Josephson-dominated tunneling.