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1.
J. Wolter P.M.Th.M. van Attekum R.E. Horstman M.C.H.M. Wouters 《Solid State Communications》1981,40(4):433-435
Current pulses larger than the critical current Ic are passed through narrow superconducting aluminium strips. The time delay between the start of the pulse and the onset of the voltage response is measured as a function of current amplitude for various temperatures (0.84<T/Tc<0.98). We find the delay time to be dependent on the temperature as (1 - T/Tc)α with α changing from a value of - 0.5 for I/Ic close to 1 to a value of - 1.0 for I/Ic larger than 3. 相似文献
2.
Summary It is shown that the behaviour of the temperature dependence of the critical current in polycrystalline thin films of high-T
c superconductors depends crucially on the assumption made concerning the nature of the intergranular material. The usual assumption
of a superconductor-insulator-superconductor (=SIS) ?sandwich? between each grain leads to a crossover fromI
c∼(1−T/T
c) toI
c∼(1−T/T
c)3/2, for temperatures nearT
c (whereI
c is the critical current,T the absolute temperature, andT
c the superconducting transition temperature). Instead, for a superconductor-normal metal-superconductor (=SNS) sandwich the
dependenceI
c∼(1−T/T
c)2 is found for all temperatures. Consideration is given to the effect of self-magnetic field on the analysis. The comparison
between expressions for continuous and granular systems is extended.
Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction. 相似文献
3.
《Solid State Communications》1987,62(5):323-326
SQUID susceptibility measurements of the high Tc superconductor Sr0.2La1.8CuO4, with a 40 K resistive onset, are reported for fields from 1 μT to 4.5 T (10 mG to 45 kG). Data show an average lower critical field of 30 mT at 5 K, but with nonlinearities appearing as low as 100 μT. Zero field cooling and subsequent application of a field shows a diamagnetic shielding effect reaching 100% in the lowest fields with a 37 K onset and 31 K midpoint. The observed Meissner effect in single phase material exceeds 40% but decreases with oxygen annealing even though Tc increases. 相似文献
4.
We have investigated the current-induced step-like structure in theV?T andV?I characteristics of tin whiskers with a mean free pathl for the electrons which is reduced by indium impurities (up to 3.6 at %). The extrapolation of theV?I characteristics beyond the first voltage step shows a zero-voltage interceptI 0≈0.5I c (I c=critical current). From the differential resistance beyond the first voltage step a lengthL An1 can be obtained which is proportional tol 1/2. These results can be understood by assuming phase-slip centers in the whisker which carry a time-averaged supercurrent of approximately 0.5I c above the critical current, and at which a voltage is developed by the “healing” of nonequilibrium quasiparticles. 相似文献
5.
M. Wurlitzer F. Mrowka P. Esquinazi K. Rogacki B. Dabrowski E. Zeldov T. Tamegai S. Ooi 《Zeitschrift für Physik B Condensed Matter》1996,101(4):561-564
We have studied the hysteretic loss and the shielding capability of Bi2Sr2CaCu2O8and YBa2Cu4O8 crystals as a function of ac field (μ 0 H ≤ 1mT), frequency, and temperature at small dc fields (μ0 H a < 1 mT) near the critical temperature T c . We show that the global ac field dependence of the susceptibility can be described in terms of a geometrical barrier model in agreement with local permeability results. At temperatures very near T c , however, we observe a crossover to diffusive behavior. The frequency dependence of the temperature of the dissipation maximum at finite dc fields shows a thermally activated behavior. 相似文献
6.
B. I. Smirnov T. S. Orlova A. N. Kudymov M. T. Lanagan N. Chen K. C. Goretta 《Physics of the Solid State》1997,39(11):1759-1761
An experimental study is reported of the influence of temperature (T), electric field polarity (±E), as well as of changes in the electrode/insulator/superconductor (E/I/S) measuring system on the field effect in the ceramic (BiPb)2Sr2Ca2Cu3Ox. It has been established that at 77 K and for E⩾60 MV/m the critical current I
c and conductivity of the sample increase for I>I
c, irrespective of the field polarity. For lower fields and a negative electrode potential the conductivity in an electric
field may decrease. The field effect decreases with increasing temperature, to practically vanish near T
c where the sample is still in superconducting state. Experiments carried out with more complex systems E/I/M/I/S and E/I/M/S (M stands for a metallic foil) support the conclusion that it is the external electric field that is responsible for the observed
effects.
Fiz. Tverd. Tela (St. Petersburg) 39, 1967–1970 (December 1997) 相似文献
7.
B. I. Smirnov T. S. Orlova S. Sengupta K. C. Goretta 《Physics of the Solid State》2000,42(7):1207-1210
The effect of an electric field E=120 MV/m in the electrode-insulator-superconductor system on I–V curves obtained at 77 K on two types of single-crystal samples cut from monolithic superconducting YBa2Cu3Ox/Y2BaCuO5 has been studied. The Y211 nonsuperconducting phase in the ingot was in the form of precipitates ≈1 μm in size. It has been
found that an electric field applied to samples with a comparatively low Y211 content (volume fraction 8%) does not affect
the critical current I
c
while reducing the resistance R at currents slightly above I
c
. In samples containing more than 35% Y211 phase, electric field results in an increase of I
c
and a decrease of R for I>I
c
. Data on the critical temperature T
c
and the temperature dependence of I
c
have also been obtained.
__________
Translated from Fizika Tverdogo Tela, Vol. 42, No. 7, 2000, pp. 1172–1175.
Original Russian Text Copyright ? 2000 by Smirnov, Orlova, Sengupta, Goretta. 相似文献
8.
M. Rosenberg M. Mittag R. Job W. Chojetzki R. Wernhardt H. Sabrowsky R. Neubauer 《Zeitschrift für Physik B Condensed Matter》1987,69(2-3):151-157
From the temperature dependence of the specific heat of the semiconductor La2CuO4 and the high temperature superconductors La1.8Sr0.2CuO4 (T c =37.2 K) and YBa1.9K0.1Cu3O6.9 (T c =91.5 K) in the range 1.5–30 K, a strong similarity of the lowfrequency part of their phonon density of states with a peak around 10 meV could be inferred. In the case of La1.8Sr0.2CuO4 the thermodynamical critical field belowT c has been determined and using the Rutger's formula and the BCS model, a Sommerfeld coefficient γ=9 mJ·mol?1 K?1 was obtained, which, taking into account recent results of band structure calculations leads to an electron-phonon enhancement factor γ=1.3, value compatible withT c =36 K when using McMillan's formula forT c . A systematic study of the magnetization offered evidence for strong flux trapping effects at higher fields and for Meissner shielding by superconducting Josephson currents in fields below 6 mT at 4.2 K. 相似文献
9.
N.M. Strickland E.F. Talantsev N.J. Long J.A. Xia S.D. Searle J. Kennedy A. Markwitz M.W. Rupich X. Li S. Sathyamurthy 《Physica C: Superconductivity and its Applications》2009,469(23-24):2060-2067
Linear damage tracks are created in production-quality YBCO coated conductors by irradiation with 61–74 MeV Ag ions. The ion tracks are observed by transmission electron microscopy to be elongated but discontinuous. The in-field transport critical current (Ic) is enhanced significantly for fields applied parallel to the irradiation direction with a broad peak appearing in the magnetic field-angle dependence of the critical current, coinciding with the irradiation direction. The zero-field Ic is typically reduced somewhat, however annealing at 200 °C partially restores this and enhances the in-field Ic even for field parallel to the irradiation direction. Lower energies tend to produce a weaker peak, but also retain the zero-field Ic to a greater extent, consistent with a trend of greater discontinuity in the ion tracks. 相似文献
10.
Y. Takahashi Y. Yoshida Y. Ichino Y. Takai Y. Takahashi M. Yoshizumi T. Izumi Y. Shiohara T. Kato 《Physica C: Superconductivity and its Applications》2011,471(21-22):937-939
We have reported SmBa2Cu3Oy (SmBCO) films on single crystalline substrates prepared by low-temperature growth (LTG) technique. The LTG-SmBCO films showed high critical current densities in magnetic fields compared with conventional SmBCO films prepared by pulsed laser deposition (PLD) method. In this study, to enhance critical current (Ic) in magnetic field, we fabricated thick LTG-SmBCO films on metal substrates with ion-beam assisted deposition (IBAD)-MgO buffer and estimated the Ic and Jc in magnetic fields.All the SmBCO films showed c-axis orientation and cube-on-cube in-plane texture. Tc of the LTG-SmBCO films were 93.1–93.4 K. Jc and Ic of a 0.5 μm-thick SmBCO film were 3.0 MA/cm2 and 150 A/cm-width at 77 K in self-field, respectively. Those of a 2.0 μm-thick film were 1.6 MA/cm2 and 284 A/cm-width respectively. Although Ic increased with the film thickness increasing up to 2 μm, the Ic tended to be saturated in 300 A/cm-width. From a cross sectional TEM image of the SmBCO film, we recognized a-axis oriented grains and 45° grains and Cu–O precipitates. Because these undesired grains form dead layers, Ic saturated above a certain thickness. We achieved that Ic in magnetic fields of the LTG-SmBCO films with a thickness of 2.0 μm were 88 A/cm-width at 1 T and 28 A/cm-width at 3 T. 相似文献
11.
Measurements of critical currentsI
c, transition temperaturesT
c, as well as transmission electron microscopy, scanning electron microscopy and X-ray analysis have established a correlation between critical currentI
c, the tape heating temperature during deposition, and the presence of a fine dispersion of precipitates. As the tape heating current (temperature) increased from 3 to 5 Amps,I
c increased from 20 to 430 Amps/3 mm tape width at 50 kG. A fine precipitate of the Nb2N phase was observed for highest tape heating temperatures. It is concluded that the precipitate particles may act as flux-pinning centers in the Nb3Sn layer. 相似文献
12.
采用Green函数技术,我们讨论了温度从T=0直到T=Tc范围内铁磁体表面和界面的磁化强度随温度的变化情况,所得到表面磁化强度的结果与其他作者的结果一致;而在界面计算中,我们发现界面的Tc与体内的不同,并且找到了一个关系式:TccA,TcB)。
关键词: 相似文献
13.
The quasi-multilayer films of YBa2Cu3O7−δ
/YSZ (YSZ denotes Yttria Stabilized Zirconia) are prepared by means of pulsed laser deposition (PLD), and a systematic study
of the magnetic-field and temperature dependence of the critical current density J
c(H,T) for the YBCO/YSZ quasi-multilayer film is presented. Angular-dependent J
c(H,T) measurements have demonstrated that the growth control strategy is very effective in preventing the vortex motion at high
fields and high temperatures. The temperature dependence of isotropic and anisotropic contribution to J
c is investigated in order to evaluate the strength of the defects. It is suggested that at high applied fields (such as 7
T), the pinning contribution of the YBCO/YSZ quasi-multilayer is dominated by the anisotropic disorders, while at intermediate-low
fields (such as 1 and 3 T) the pinning contribution is determined by both isotropic and anisotropic disorders. 相似文献
14.
A. A. Bykov I. V. Marchishin A. K. Bakarov Jing-Qiao Zhang S. A. Vitkalov 《JETP Letters》2007,85(1):63-66
The effect of dc current I dc on the electron transport in a GaAs quantum well with AlAs/GaAs superlattice barriers is studied experimentally at a temperature of 4.2 K in magnetic fields up to 2 T. A sharp increase in resistance R xx is observed in magnetic fields higher than the critical field B c. The value of B c is found to decrease with increasing the current I dc. The phenomenon observed in the experiment is qualitatively explained by the electric breakdown of superlattice barriers under the action of the Hall field. 相似文献
15.
G. N. Mikhailova E. I. Demikhov V. P. Aksenov L. Kh. Antonova L. D. Iskhakova L. N. Zherikhina E. A. Kostrov S. V. Lavrishchev V. S. Mikhailov A. V. Troitskii A. M. Tskhovrebov 《Technical Physics》2009,54(2):235-238
The stability of critical parameters T c and I c of commercial high-temperature superconducting wires upon long-term passage of transport current (about 0.7I c) in liquid nitrogen (77 K) is studied. Voltage-current characteristics U(I), as well as the critical current and critical temperature, are investigated for the case of Bi(2223) hermetic multifilament wires and Dy(123) superconducting tapes covered by a thin Ag layer. In the former case, a considerable decrease in the critical current (by ~30%) and swelling of the wires after passage of the current for 323 h are observed. The same is true for a reference sample, which does not experience the action of current and stays in liquid nitrogen for 700 h. The decrease in the critical current in the Bi(2223) sample is likely to be associated with penetration of a liquid coolant into the composite conductor: evaporating and expanding as a result of heating, it severely deforms the material. The Dy(123) sample grown epitaxially demonstrates high stability of the critical current after it has experienced the action of current for 400 h and been kept in liquid nitrogen for 1000 h. 相似文献
16.
17.
18.
《Physica C: Superconductivity and its Applications》1999,311(1-2):65-74
Nanometer SiC particles were added to (Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) precursor powders and the powders were transformed into silver-sheathed superconducting tapes by the standard powder-in-tube (PIT) technique. The influence of SiC on the melting temperature, high-Tc (Bi2223) phase formation, microstructure and transport property of the tapes was studied by means of DTA, XRD, SEM/EDX, electrical and magnetic measurements. The results showed that SiC addition lowered the melting temperature of the superconductor powders and consequently, decreased the optimum sintering temperature of the tapes. However, the addition did not affect the Bi2223 phase formation and critical temperature (Tc) of the tapes up to 1.00 wt.% of SiC. Most importantly, the addition of a small amount of SiC (0.15 wt.%) improved the critical current (Ic) and Ic behavior in magnetic field as a result of the enhancement in density, grain alignment, grain connectivity and flux pinning of the tapes. 相似文献
19.
20.
The thermo-emf ΔV and thermoelectric current ΔI generated by imposing a temperature gradient alternating at a period of T on a thermoelectric (TE) generator were measured as a function of t, where t is the lapsed time and 1/T was varied from 0 to 1/30 s-1. A TE generator was sandwiched between two Peltier modules connected in series. The alternating temperature gradients were produced by imposing an alternating voltage V on two Peltier modules, where V was varied from 1.0 to 3.7 V. Both ΔV and ΔI generated by the TE generator oscillate at a period of T but their amplitudes tend to increase monotonically with an increase of V. The effective thermo-emf ΔVeff and current ΔIeff calculated from ΔV and ΔI increase abruptly with an increase of 1/T and have a local maximum at 1/T=1/120 or 1/240 s-1. The generating power ΔWeff(=ΔVeffΔIeff) tends to increase proportionally with an increase of input power Winput, owing to the increase in the temperature difference. The rate of ΔWeff to Winput at 1/T=1/240 s-1 reached approximately 3.2 times as large as that obtained for the steady temperature gradient corresponding to 1/T=0 s-1. It was thus found that the generating power of the TE generator operating under the temperature gradient alternating at an optimum period is remarkably increased compared to that of a TE generator working under a conventional steady temperature gradient. PACS 72.15.Jf; 84.60.Rb; 85.30De 相似文献