Y.D. Dai

The supercurrent spatial distribution of grain boundary junctions

Abstract We carried out a series of measurement on several different sizes of YBCO grain boundary junctions by using an improved method, in which we used the resistively shunted junction (RSJ) model to get a more accurate I c ( B ) relation regardless of the magnitude of the critical current. From the I c ( B ) dependence of the YBCO GBJs the supercurrent distribution are derived. For the latter a spatial resolution of about 0.4 μm is obtained. The measured correlation function shows that the supercurrent density across the grain boundary is spatially inhomogeneous on even μm scale.

Antiferromagnetic ordering in the high-Tc superconductors (Y1−xGdx) Ba2Cu3O7−y

Abstract A systematic study of structure, superconductivity, and magnetic properties of (Y 1−x Gd x ) Ba 2 Cu 3 O 7−y was carried out. The susceptibility of YBa 2 Cu 3 O 7−y above Tc is nearly independent of temperature. For all Gd-substituted samples, Gd exhibite the same effective magnetic moment of 7.75 μ B . Antiferromagnetic ordering temperature is 2.3K and 1.7K for x=1.0 and 0.8, respectively. Antiferromagnetic ordering was not observed for x ≤ 0.6 down to 1.5K.

Nonlinear voltage response due to thermal noise of Josephson junction

Abstract The effects of thermal fluctuations on the Josephson effect in a junction with finite capacitance are studied in the framework of two variables Fokker-Planck equation of Brownian motion. A general analytic stationary solution is obtained. Comparison with experimental data of YBCO junctions as well as BSCCO single crystals is shown with satisfactory agreement.

Influence of high frequency cut-off on application of hight Tc SQUID in transient electromagnetic method

Abstract We have evaluated the influence of high frequency cut-off on applications of SQUID in transient electromagnetic method. Numerical integral was employed to demonstrate the influence of frequency cut-off. A theoretical interpretation to the computation outcome is also given.

TEM study of microstructure of YBa2Cu3Oy bicrystal grain boundary junctions grown on Y2O3 stabilized ZrO2 bicrystal

Abstract The microstructure details of bicrystal boundaries of both the YBa 2 Cu 3 O y thin film and the ZrO 2 bicrystals substrate were studied by means of transmission electron microscopy (TEM).

Direct observation of remnant fields in Y2BaCuO5 and platinum doped YBa2Cu3O7 bulk superconductors

Abstract The dynamic decay process of the remnant field and the thermally activated flux creep in the melt texture growth Y2BaCuO5 and platinum doped YBa2Cu3O7 bulk samples were directly observed. The doping effect of Y2BaCuO5 and platinum on the trapped flux was clearly watched.

Anomalous resistive oscillations in mesoscopic Al superconducting wires

Abstract Oscillations in R–T curves of mesoscopic Al wires near superconducting transition temperature were observed under weak AC currents. We attribute this observation to the non-equilibrium superconductivities near the N–S interfaces and the movement of these interfaces.

The interaction of phase slip centers in mesoscopic aluminum line

Abstract The I – V characteristics of mesoscopic aluminum wire have been studied. We found step structures in the I–V characteristics, which we believe are due to the formation of phase slip centers. With decreasing temperature, the step structure is replaced by peak structure. This anomalous behavior was analyzed in terms of the interaction between the phase slip centers.

Modified hairpin λ/2 resonator for high Tc SQUID

Abstract In order to understand the nature of the hairpin resonator suggested by Zhang et al. [IEEE Trans. Appl. Supercond. (1996)], we have investigated a circuit with the similar structure. It is found that the tank circuits manifested the behaviour of λ/2 resonator, instead of an LC one. The resonant frequency agrees with the prediction of theory for transmission line. We have found the data reported by Zhang et al. are also consistent with the relation. This understanding enables us to design a λ/2 resontor of the transmission line with a desired resonant frequency and a proper impedance to match the readout electronic easily.

Microwave induced steps of high performance grain-boundary junctions of YBa2Cu3O7

Abstract We have studied the microwave induced steps of the grain-boundary junctions fabricated with epitaxial superconducting YBa 2 Cu 3 O 7 thin films on bicrystal substrates. Clear steps up to N =46 were observed in the current-voltage characteristics at liquid nitrogen temperature. The comparison between the prediction of RSJ model has been made and the structure non-uniformity is introduced to interpret the discrepancy of step-height as a function of microwave amplitude.