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HIGH FREQUENCY ELECTRICAL TRANSPORT MEASUREMENTS OF NIOBIUM SNS JOSEPHSON JUNCTION ARRAYS AND NIOBIUM THIN FILMS WITH NANOSCALE SIZE MAGNETIC DOT ARRAY

GOMEZ, LUIS BELTRAN
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054743123

Abstract Details

2003, PhD, University of Cincinnati, Arts and Sciences : Physics.
In this dissertation, measurements on two different niobium (Nb) based systems, namely superconductor-normal-metal-superconductor (SNS) Josephson junction arrays (JJA), and thin Nb films with nanoscale size magnetic dot arrays, are presented. Without high frequency (rf) signals at nearly zero magnetic field, these measurements show similarities for the two systems. These similarities are explained by proposing that very close to the critical temperature (Tc) of the Nb film sample, the stray magnetic field of the dots reduces the superconductivity in the film to make it a perconductor-weaker-superconductor-superconductor (SS’S) JJA. With rf signals, their dc-voltage-current characteristics (VI’s) show the appearance of constant voltage steps known as Shapiro steps. For SNS-JJA, the dependence of the width of the steps (Delta-I-n) on the amplitude of the rf current (Irf) is Bessel-function-like. The maximum width of the first step ([Delta-I-1]MAX) was found to increase as a function of rf frequency (frf) reaching a maximum for frf~1.8 times the array’s Josephson frequency (fc). This maximum was maintained for frf>4.9fc. Also, in JJA with missing junctions, [Delta-I-n]MAX was smaller, disappearing for frf~fc. For Nb films near Tc, no Bessel-function-like oscillations were observed for Delta-I-n. Also, Delta-I-0 (or critical current, Ic) showed a maximum for Irf different from 0, contrary to what was found in SNS-JJA, falling to zero for higher Irf. This enhancement of Ic with Irf was attributed to non-equilibrium superconductivity mechanisms near Tc. Observation of higher order steps (n=1,2,3,etc) became evident only from the dynamic resistance (dV/dI)vs.V plots (where a step corresponds to a minima for this curve). The first step was most evident for Irf values that made Delta-I-0=0. At these values, V1 (the voltage that corresponded to the first minimum in the dV/dIvs.V curve) satisfied the Josephson relation V1=N(h/2e)frf, where N is the number of “junctions” in the direction of the current. At fixed frf, V1 was found to increase with Irf. This result was interpreted as having more junctions participating in the steps formation, which was attributed to magnetic interactions among the dots magnetic moments and with the Irf to minimize the total energy of the system.
Dr. David B. Mast (Advisor)
130 p.
S Niobium; Josephson junction arrays; High Frequency Transport Measurements; thin films; magnetic dots

Recommended Citations

Citations

  • GOMEZ, L. B. (2003). HIGH FREQUENCY ELECTRICAL TRANSPORT MEASUREMENTS OF NIOBIUM SNS JOSEPHSON JUNCTION ARRAYS AND NIOBIUM THIN FILMS WITH NANOSCALE SIZE MAGNETIC DOT ARRAY [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054743123

    APA Style (7th edition)

  • GOMEZ, LUIS. HIGH FREQUENCY ELECTRICAL TRANSPORT MEASUREMENTS OF NIOBIUM SNS JOSEPHSON JUNCTION ARRAYS AND NIOBIUM THIN FILMS WITH NANOSCALE SIZE MAGNETIC DOT ARRAY. 2003. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054743123.

    MLA Style (8th edition)

  • GOMEZ, LUIS. "HIGH FREQUENCY ELECTRICAL TRANSPORT MEASUREMENTS OF NIOBIUM SNS JOSEPHSON JUNCTION ARRAYS AND NIOBIUM THIN FILMS WITH NANOSCALE SIZE MAGNETIC DOT ARRAY." Doctoral dissertation, University of Cincinnati, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054743123

    Chicago Manual of Style (17th edition)

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© 2003, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.