Strong Proximity Effect Research Articles

Time dependence of ac losses in multifilamentary NbTi superconductors due to proximity coupling

The ac losses of NbTi multifilamentary superconducting wires with a copper matrix were measured using a sensitive calorimetric method. The wire samples, which have filament diameters in the micrometer range and interfilament spacings of a few tenths of a micrometer, exhibit a strong proximity effect. The measured power loss at a constant ac field amplitude and frequency showed an unexpected time dependence on a very long time scale of hours, compared to the ac field cycle time being in the millisecond range. The measured loss vs time curves were found to depend sensitively on amplitude and frequency of the ac field, and in the way the ac field was switched on. The effect can be rather large, changes of losses by up to 60% were found. Losses can increase or decrease with time depending on the structure of the sample. As an independent check losses were also measured by a magnetization method. The results were in very good agreement with the calorimetric measurement. The effect of time dependent losses is qualitatively explained by the slow decay of proximity currents which are induced when the ac field is switched on. They create a time dependent bias magnetization, which influences the ac losses.

Unexpected time dependence of ac losses in multifilamentary NbTi superconductors

Losses of NbTi multifilament superconductors in a copper matrix in alternating magnetic fields were measured using a specially developed sensitive calorimetric method. The investigated samples have filament diameters in the micrometer range and exhibit a strong proximity effect. The measured losses at fixed ac frequency and field amplitude showed an unexpected time dependence on a very long time scale of hours, compared to the ac field cycle time, which was in the millisecond range. This time dependence is probably a consequence of slowly decaying proximity currents.

Single-particle tunneling and Josephson effect in Bi-Sr-Ca-Cu-O:Pb and Tl-Ba-Ca-Cu-O compounds

Abstract The experimental I (V)-characteristics of break junctions for monocrystalline BiSrCaCuO: Pb (2212- phase), polycrystalline (2223- phase) samples and for samples with the “intergrowth” of 2212- and 2223- phases have been investigated. On the I (V)- characteristics of break junctions for samples with the “intergrowth” of phases a vertical current raise at V=±2 δ /e and a “knee”- structure typical for S 1 S 2 IS 2 S 1 - systems have been observed. The temperature dependence of gap parameter δ points to the strong proximity effect in these junctions.

SQUID operation of point contacts from YBaCuO

dcSQUID operation of YBa 2Cu 3O 7−y is investigated using point-contact devices. Special attention is paid to the indications of strong proximity effect in YBaCuO-tin point contacts. Investigations of heterocontacts between YBaCuO and tin, and between niobium and tin, are presented, both above and below the critical temperature of tin.

Current-voltage characteristics of a four-terminal superconducting weak link

The current-voltage characteristics of a new type of Josephson-like junction consisting of four superconductors in connection with a common region via separate weak links are investigated. This arrangement permits strong interaction and proximity effects to occur inside the composite junction, and the observed variations in theI–V curves can be explained mainly in terms of an exchange of dc and ac quasiparticle currents between phase-slip centers. In particular, direct frequency locking among three Josephson oscillators and induced dc voltage in an unbiased junction have been found for the first time. These effects are of interest for considerations of developing large-scale integrated superconducting circuits.

Observation of proximity- and non-equilibrium effects in ternary heavy ion reactions

Kinematically complete experiments have been performed on the two- and three-body exit channels in the reactions84Kr+166Er and129Xe+122Sn at 12.5 MeV/u. Three-body events occur with an unusually high probability. They arise from a fast two-step mechanism where a sequential fission-like process follows a deep inelastic collision with preferentially very large energy losses. Strong Coulomb proximity effects are observed in the three-body final state which, treated quantitatively in Coulomb trajectory calculations, establish a time-scale of 1·10−21 s between the consecutive scission acts. The angular distribution of fission fragments is consistent with an orientation of the fission axis approximately collinear with the axis of the first scission, and the mass distribution of the fission is asymmetric with the heavier mass emitted preferentially opposite to the direction of the third particle. The high fission probability, the short time-scale, the near collinear orientation and the fission mass asymmetry together present consistent evidence for a new phenomenon of non-equilibrium fission.

Shielding Properties of Isolated-Phase Bussystems

The shielding effectiveness of an isolated-phase bus with continuous enclosures depends on a number of parameters. To study this problem we developed a system to measure amplitudes and phase angles of the currents in an isolated-phase bus during regular operation in a power plant. In our theoretical description we give new inductance values for three cylinders in situations with strong proximity effects. The flux near the short-circuiting ircuiting end connection is strongly influenced by the currents and fields outside the bussystem. Good agreement ent between calculated and measured sheath currents is reported for three bussystems. The asymmetry between the currents in the two outer sheaths is explained.

Shielding Properties of Isolated-Phase Bus Systems

The shielding effectiveness of an isolated-phase bus with continuous enclosures depends on a number of parameters. To study this problem we developed a system to measure amplitudes and phase angles of the currents in an isolated-phase bus during regular operation in a power plant. In our theoretical description we give new inductance values for three cylinders in situations with strong proximity effects. The flux near the short-circuiting ircuiting end connection is strongly influenced by the currents and fields outside the bussystem. Good agreement ent between calculated and measured sheath currents is reported for three bussystems. The asymmetry between the currents in the two outer sheaths is explained.

Direct Observation of Proximity Effects in Ternary Heavy-Ion Reactions

Kinematically complete experiments have been performed on the two- and three-body exit channels in 12.4-MeV/u $^{84}\mathrm{Kr}$ on $^{90}\mathrm{Zr}$ and $^{166}\mathrm{Er}$, and 12.5-MeV/u $^{129}\mathrm{Xe}$ on $^{122}\mathrm{Sn}$. Three-body events occur with a high probability. They arise predominantly from two-step reactions, with large energy losses in the first step leading to fission in the second. Strong proximity effects, observed in the final three-body state of the Xe-Sn reaction, establish a scission-to-scission time of about 1\ifmmode\times\else\texttimes\fi{}10$^{\ensuremath{-}21}\mathrm{s}$.

Superconductivity in Cu-V-Si alloys

The superconducting properties of copper ternary alloys containing small amounts of vanadium and silicon have been investigated. The wire samples of three alloys: Cu/sub 90/V/sub 7.5/Si/sub 2.5/, Cu/sub 88/V/sub 9/Si/sub 3/, and Cu/sub 84/V/sub 12/Si/sub 4/: show a resistive superconducting transition around 17 K, the characteristic transition temperature of the A15 compound V/sub 3/Si, followed by a plateau and a second transition between 5 and 10 K. The resistivity, however, does not drop to zero down to 2.5 K. The maximum drop in resistivity is observed for the alloy containing minimum amounts of vanadium and silicon. Complete superconductivity is absent in these alloys for two reasons. First the effective superconducting volume fraction in these alloys is well below the threshold value obtained by either the effective medium theory or the site percolation theory for solid conduction. Second, the superconducting phase does not precipitate in a fine structure in the matrix and a strong proximity effect does not operate. Experimental evidence confirms the formation of brittle phase V/sub 3/Si in the cast alloys which does not get elongated to the same extent as the matrix when rolled or drawn. This reduces the effective volume fraction of V/sub 3/Si in the drawnmore » wires. Annealing of these wires causes the superconducting particles to coalesce and grow in size, increasing the interparticle distances to the detriment of superconductivity in these alloys.« less

Mécanismes de piégeage et effets de proximité dans des échantillons monograins d'alliages eutectiques lamellaires orientés

2014 Magnetization measurements, carried out on monograined bulk samples of a lamellar Pb-Sn eutectic alloy for lamellar spacings aE in the range 1.5 03BCm to 5 03BCm, have shown that the Sn lamellae remain diamagnetic up to 7 K, which proves the existence of a very strong proximity effect. The magnetization curves can be explained assuming a preponderant pinning at the numerous Sn/Pb interfaces. The Ic(H) curves obtained on Pb-Sn or ln2Bi-In 20 03BCm thick films having a perfect lamellar structure (1.5 03BCm aE 10 03BCm ; I // lamellae ; H // lamellae and I) exhibit a peculiar behaviour in the small-field range : Ic remains constant for fields increasing up to a certain value H1 (~ 50 Oe at 4.2 K). This behaviour can be related to the successive potential barriers, due to the interfaces, for the vortices. The major role of these interfaces is confirmed by the study of the bulk pinning force Fp(b) ~ b1⁄2(1 b), b = H/Hc2 ; this peculiar b dependence is indeed typical of pinning at N/S boundaries. LE JOURNAL DE PHYSIQUE TOME 38, AVRIL 1977,

Strong Proximity Effects in Cu: Superconductivity of a Fine Nb–Cu Composite

The magnetic behavior of composites of very fine (less than 1000 Å) niobium wires in copper matrices has been measured at temperatures below 10°K. Three Meissner effects were observed, two of which were apparently due to strong proximity effects in the copper. The temperature dependence of the magnetization curve and measurements of the real and imaginary components of zero-field ac susceptibility agree. The geometry and properties of the composite, which are known in some detail, are used together with current models for proximity effects to develop an adequate explanation of the data.