Magnetic properties of two-dimensional SNS-type Josephson junction arrays

JETP Letters - The field dependence of the magnetic moment of square (100×100) SNS-type Josephson junction arrays was studied by a SQUID magnetometer. A considerable difference in the behavior...     

Shock wave working of high-TC superconductors

Abstract

The results of investigating the processes of explosive compaction of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O powdered ceramic high temperature superconducting materials and the shock-induced variation of their properties are presented. The possibility for obtaining metal-ceramic cylinder and spiral-shaped articles is illustrated. The shock wave loading of sintered ceramics is shown to result in degrading its superconducting properties up on R(T), which are subsequently restored by low-temperature annealing. The loss of superconducting properties is demonstrated to correlate with the X-ray lines width. In case of Bi-4334 ceramic, we have observed the improving SP-properties on susceptibility just after shocking it. The effect of the compaction pressure, initial particle size, atmosphere (air, O₂, N₂), initial temperature on material properties is studied.     

Impurity absorption of SrS-Ce3+ phosphors

We investigate the impurity absorption of SrS−Ce phosphors. For this purpose, we measure the spectra of diffuse reflection of powder phosphors. It is established that the introduction of Ce simultaneously with a coactivator gives rise to a strong absorption band at 2.88 eV, and the introduction of a coactivator (NH₄F, NH₄Cl, NH₄Br, NH₄I, LiCl, NaCl or KCl), to an absorption band at about 2.36 eV. We assume that the absorption band at 2.88 eV is caused by that portion of Ce introduced that forms the center of luminescence of Ce³⁺. Tartu University, Estonian, Republic, 18, Yulikooli St., Tartu, EE2400, Estonia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 542–544, July–August, 1997.     

Magnetic moment of square SIS Josephson arrays: Self-organized criticality

The temperature-and magnetic-field dependences of the magnetic moment of square Josephson arrays with SIS-type junctions are studied experimentally. Two temperature regions are observed with different types of magnetization curves. Magnetic flux avalanches are detected in the low-temperature region. Statistical analysis of avalanche amplitudes A shows that their size distribution varies in accordance with the power law P∝Aⁿ with crossover, when exponent n varies from n=?0.7 for small avalanches to n=?6 for large avalanches, while the frequency spectrum varies in accordance with the law 1/f^α. Such behavior is interpreted as a manifestation of self-organized criticality.     

Statistics of avalanches in the self-organized criticality state of a Josephson junction

Magnetic flux avalanches in Josephson junctions that include superconductor-insulator-superconductor (SIS) tunnel junctions and are magnetized at temperatures lower than approximately 5 K have been studied in detail. Avalanches are of stochastic character and appear when the magnetic field penetration depth λ into a junction becomes equal to the length a of the Josephson junction with a decrease in the temperature. The statistical properties of such avalanches are presented. The size distribution of the avalanches is a power law with a negative noninteger exponent about unity, indicating the self-organized criticality state. The self-organized criticality state is not observed in Josephson junctions with a superconductor-normal metal-superconductor (SNS) junction.     

A nonparametric scaling equation of state for liquids

A new nonparametric scaling equation of state is suggested. The equation correctly describes the p-ρ-T data and heat capacities of liquids close to the critical vaporization points. It was obtained with the use of the S spinodal and the mixing of scaling fields as a first approximation (asymmetric and nonasymptotic terms were ignored). The new equation was used to approximate the data on ⁴He, C₂H₄, and H₂O in the critical region. The results showed that it correctly described the critical behavior of thermodynamic functions, including isochoric heat capacity, not only in the asymptotic but also over a fairly wide density region at the critical point. The suggested equation of state describes the p-ρ-T data with the same error as the Schofield parametric equation of state. The new equation, however, better reproduces the behavior of heat capacities and is much simpler to use. As distinct from the Schofield equation, the new equation, like classic equations of state, allows the spinodal to be determined from the (?p/?v) _T = 0 condition at T < T _c .     

Universal phenomenon of self-organized criticality in magnetic flux dynamics

Magnetization curves of square arrays of Josephson junctions of two basic types were investigated: superconductor–insulator–superconductor (SIS) and superconductor–normal metal–superconductor (SNS).

Magnetic flux avalanches were observed in SIS arrays. A statistical analysis of flux avalanches showed that their size distribution can be described by a power law with a crossover where the exponent n varies from −1.2 for small avalanches to −3.5 for the large ones. Such a behavior of avalanches is interpreted as the self-organized criticality (SOC) manifestation. In SNS arrays, the flux avalanches were not observed, but a considerable asymmetry of a hysteresis curve was revealed.