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The temperature dependence of the local structure of liquid Sb has been studied by x-ray absorption spectroscopy. It is shown that about 10% of the atoms with coordination of 3 and weak Peierls distortion exist in liquid Sb just above its melting point. The Peierls distortion weakens gradually with increasing temperature and vanishes at about 750 degrees C. This structural variation in liquid Sb is different from the normal liquid-liquid phase transition. This work reveals the relationship between the variation in the local structure and the change in the physical properties, such as the electrical resisitvity of liquid Sb, with temperature. The complete agreement between the measured electrical resistivity values during heating and cooling processes suggests that the structural units with the features of a rhombohedron appear above the melting point of Sb during solidification. (c) 2008 American Institute of Physics.

Epitaxial Ti2Ba2CaCu2Ox thin film dc superconducting quantum interference devices (dc SQUIDs) have been fabricated on bicrystal SrTiO3 (STO) substrates. By using the Tl-2212 single phase film, a flux noise density, S-Phi(1/2), of 2.0 x 10(-5)Phi(0) Hz(-1/2) at liquid nitrogen temperature was obtained in the white noise region, which is more than one order of magnitude lower than previous Tl-based SQUIDs made by multiphase thin films. The Tl-2212 thin film bicrystal grain boundary Josephson junctions have demonstrated resistively shunted junction (RSJ) behaviour. The characteristic voltage, VC, which is the product of critical current I-C and junction resistance R-N, was 45 muV at 95 K. The dependence of the critical current on temperature near T-C ( 105 K) was measured as I-C(T) similar to (1 - T / T-C)(1.5-1.98). The dc SQUIDs can operate at temperatures up to 99 K.

We present an analytical investigation on the spontaneous magnetization of infinitely large two-dimensional identical hexagonal superconducting pi-ring arrays based on an ansatz that each of the pi-rings carries a magnetic flux with the same frustration index. The free energies per ring, U-n, in various states characterized by the number of zero-current ('quiet') junctions n in the ring are calculated. A ladder relation of the energies has been demonstrated as U-0 < U-1 < U-2 < U-3 < U-4 < U-5 less than or equal to U-6, which basically shows that the fewer the quiet junctions of a state, the more favourable the energy for the state formation. This result is in qualitative agreement with the recent experimental observations in the large-scale hexagonal pi -loop (triangular half flux quantum) array (Hilgenkamp et al 2003 Nature 422 50-3).

Large planar arrays of Josephson junctions form two-dimensional systems with many interesting properties, especially arrays containing superconducting π-junctions with unconventional superconducting d-wave symmetry. Here we present an analytical investigation of spontaneous magnetization in two-dimensional superconducting π-ring arrays, starting from an ansatz that each of the identical π-rings carries a magnetic flux with the same frustration index. Our results show that the flux structure with full antiparallel spontaneous magnetization is the most favourable of all possible arrangements in both square and triangular ring arrays. In a hexagonal π-ring (triangular flux) array, although there is no full antiparallel flux pattern, the antiparallel bond of nearest-neighbour spontaneous magnetization fluxes is still energetically favourable. These results are in agreement with those recently observed experimentally by Hilgenkamp et al (2003 Nature 422 50–3) in a triangular flux array.

Properties of the superconducting surface CuO2 double layers of a cleaved Bi2Sr2CaCu2O8+delta (BSCCO) crystal in contact with An metal films are studied using mesa-structured intrinsic Josephson junctions. We show that a well-defined and experimentally controllable BSCCO/Au contact can be achieved by the stabilization of the (interstitial) oxygen atoms in the surface BiO layers at liquid nitrogen temperature during fabrication. The surface CuO, double layers are found to be in a metallic contact with An films and have a transition temperature T-c' of similar to80 K for a BSCCO crystal with bulk T-c of 91 K. Involvement of impurity atoms or molecules in the BSCCO/Au interface is found to substantially reduce the value of T-c'. (C) 2003 Elsevier B.V. All rights reserved.

In this paper, we establish a model of the micromachined SrTiO3 substrate steps for high-T-c direct-current (dc) superconducting quantum interference devices (SQUIDs). The step angle is determined by the local ion milling rate and re-deposition rate, which is caused by back sputtering of ion milling. At dynamic balance, the maximum possible step angle is predicted to be 75degrees with an ion beam incidence angle of 45degrees, which agrees well with the measured value of 71degrees. In order to obtain a better step sidewall profile, we consider the influences of Nb metal mask micromachining. To avoid a rounded angle at the step upper corner, the minimum thickness of the Nb mask should be 440 nm when the desired step height is 300 nm. At optimized process conditions, steps with sharp, steep angles, and flawless profiles have been fabricated. Nine of the twelve dc SQUIDs thus obtained exhibited resistively shunted junction current-voltage behavior and magnetic field modulation at 77 K.

Highly reliable dc superconducting quantum interference devices (SQUIDs) in temperature with step edge junctions (SEJs) were fabricated with laser molecular beam epitaxy (L-MBE) YBa2Cu3OX thin films. The reflection high-energy electron diffraction oscillation cycles proved that the superconducting films were epitaxially grown on the atomic scale. In the dc SQUID temperature transition curves, the tail structures appear at a temperature close to the transition point. The critical current dependent temperature, I(C)similar to(1-T/T-C)(2), shows that the L-MBE SEJ behaves like an SNS type junction. The white noise level, 2.0 X 10(-5) Phi(0)rootHz at 200 Hz, triangular wave signal, critical current and other characteristics exhibit no change after 42 temperature cycles and 108 days of storage. (C) 2003 Elsevier Science Ltd. All rights reserved.

We investigate the photoinduced quasiparticle dynamics in the electron-doped superconductor La2-xCexCuO4 (LCCO) by using femtosecond pump-probe technique. A monoexponential decay function is employed to fit the data for the first 20 ps after the maximum of the signal. The relaxation time decreases with increased temperature both above and below T-c. Power function (tau proportional to T-N) is used to fit the relaxation time. N is 1.45 for above 20 K and 0.3 for below 20 K. The change of N at 20 K is. attributed to the opening of the gap. (c) 2005 Elsevier B.V. All rights reserved.

We have studied the dynamics of quasiparticles in an SS′ superconducting proximity-effect bilayer based upon McMillan's proximity-effect model. Quasiparticle scattering and recombination rates were calculated for both S and S′ films. Quasiparticle transition rates between the S and S′ films, that come out naturally from McMillan's model, were also calculated, and are discussed in particular regarding the quasiparticle trapping phenomena that have been demonstrated recently in the detector applications of superconducting tunneling junctions.

Double-microbridge DC SQUIDs have been fabricated from YBCO superconducting films by lithographically patterning technique. The voltage versus the applied magnetic field dependence of a DC SQUID has been obtained in the region of temperature from 4.2 K to 23 K, The largest output voltage of the devices used in our experiments is 3.4 uV /Φ0(Φ0 is h/2e the flux quantum). The smallest measured periodicity of the flux-voltage characteristics of the DC SQUID, 12.7 mG, is consistent with the designed value. In addition, some properties of the flux-voltage characteristics of the DC SQUIDs have been discussed.

Superconducting Bi(Pb)-Sr-Ca-Cu-O thin films are prepared on single crystal (100) MgO substrates by oxygen reactive ion beam sputtering. All the films are deposited at 400°C and annealed between 830–870°C. Annealing studies show that the film properties are very sensitive to the annealing temperature and annealing time. After annealing at 850°C for 48h, metallic film with Tc(Zero)=106K are obtained. X-ray diffraction shows the film to be highly c-axis orientation perpenticular to the substrate. We have reproducibly synthesized the Bi(Pb)-Sr-Ca-Cu-O thin films with Tc(Zero) at above 100K. The films were characterized by resistance measurements, X-ray diffraction, ICP-AES, Auger electron spectroscopy(AES) and scanning electron microscopy(SEM).

Nb/Al AlOx Ti tunneling junctions with fixed Nb and Ti thicknesses of 200 nm and Al thickness ranging from 10 to 70 nm were fabricated. Preliminary results on the measurements of I – V characteristics at T = 1.3 K are reported, and are compared with a proximity-effect model recently proposed by Golubov et al..

The superconducting properties of the TlBa 2 Ca 3 Cu 4 O 11−δ single crystals have been investigated, which included hysteresis loop and time relaxation experiments. The experimental results showed that the critical current density and the relaxation rate of the TlBa 2 Ca 3 Cu 4 O 11−δ crystals had strong temperature dependence due to thermally activated flux creep.

Through the RRT program in which six domestic Laboratories were involved, it was concluded that the maximum coefficient of variation on Ic measurement among the Laboratories at 1μV/cm 77K and zero magnetic field for the Ag-sheathed 2223 BSCCO tapes was less than 2.5%, after the measured Ic value was corrected against corresponding measurement temperature.

High quality superconducting thin films of YBaCuO and Bi(Pb)SrCaCuO were reproducibly prepared by ion beam sputtering and rf magnetron sputtering from a single bulk target or a single off-stoichiometry powder target. The substrates with (100) surfaces of YSZ, SrTiO 3 , LaAlO 3 and MgO were used. We review our work on the synthesis of these thin films obtained by both in situ deposition and postannealing method. The details of thin film growth, superconducting properties, morphology, film-substrate interdiffusions, structures and crystallinities were presented and discussed.

We have prepared two kinds of single crystals in Bi-Sr-Ca-Cu oxides by flux method;plate-like single crystals which exhibit metal to superconductor at 93 K, being the high-Tclayered compound BiSr (Ca 0.35 Sr 0.25 Bi 0.40)2 Cu 2Oy with orthorhombic structure with a=5.42 Å, b=5.44 Å and c=30.78 Å respectively, and another kind of bar-shapedbismuth-poor single crystals which is superconducting at the temperature below 82K whilebeing semiconducting above this temperature.

X-ray precession technique1 has been utilized to study the reciprocal space of the superconducting single crystal Bi 2 Sr 2 CaCu 2 O y. An average structure with space group of Pnnn and a real structure with the superspace group of [Formula: see text] or [Formula: see text] have been found for this one dimensional modulated incommensurate material. As well, a basic structure with the space group of Fmmm is derived from the experimental data.

The pressure dependence of the superconductivity of the Tl-Ba-Ca-Cu-O sample with T c >110 K was studied. It is observed that the superconducting transition temperature increases at the rate of d T co / d P≈1.83 K/GPa up to 1.8K/GPa and the gentle steps of T c are always followed by a jump of the normal state resistance which is considered exhibiting the change of some fine structure related to the Cu-O planes.

The preparation and characterization in structure and chemistry of the superconducting phases in Bi-Sr-Ca-Cu-O system are briefly summarized. The growth of the 85 K single crystal superconductor Bi2Sr2CaCu2Oy is outlined. The measurement of the anisotropic normal-state resistivities of the 85 K superconducting single crystal is presented in detail and the analysis of the incommensurate modulation in this compound is also given.

The new superconductors with zero-resistance temperature around 90K in Ln-Ba-Cu-O system (Ln=Heavy rare earth elements with the exception of Tb) have been synthesised. It has been shown that the nominal composition and preparation procedure for various heavy rare earth compounds are different from each other.

We have carried out superconducting energy gap measurements for polycrystalline perovskite-structure superconductors YBaCuO, LaSrCuO and BPBO with point contact tunneling. The tunneling conductance curves for YBaCuO, LaSrCuO and BPBO show the energy gap to transition temperature ratio 2Δ/kTc =4.7, 7.8 and 5.05 respectively, which is consistant with the strong-coupling superconductivity.

We have prepared 120 K superconductor in Tl-Ba-Ca-Cu oxide system. This 120 K superconductor has been investigated by x-ray diffraction and EDAX micro-analysis. EDAX analysis shows that the composition of this superconductor is very close to TlBa ( Ca 1−x Cu x) CuO y(x−0.3). Most of the x-ray powder diffractions including all the strong ones can be indexed according to a tetragonal structure with a=5.46 Å and c= 36.2 Å which means that the sample is nearly a single phase material.

The single crystal BCSCO superconductors have been investigated by electron tunneling with both point contacts and BCSCO/Sn junctions. A gap parameter of Δ=34meV and 2Δ/kTc=8.9 have been obtained. Various dI/dV curves including BCS-like and so-called harmonic structure have been observed. We propose to make use of proximity effect and quasiparticle interference to interpret these phenomena.