摘要:

Superconducting thin films of YBa2Cu3O7−&dgr;on (100) SrTiO3are preparedinsituby a pulsed laser deposition technique at deposition rates from 1 to 145 A˚/s. Crystallinity of the films is examined by Rutherford backscattering in the channeling mode using a 2.2 MeV He+ion beam. The backscattering minimum yield (&khgr;min) increases with the deposition rate. A &khgr;minof 3% is observed in the films deposited at the lowest deposition rate. Even at a deposition rate of 145 A˚/s, the films show good crystallinity with &khgr;minof 15%, indicating epitaxial growth. The x‐ray diffraction measurements show that the films have strongc‐axis orientation normal to the substrates. The films have metallic resistance versus temperature behavior with zero resistance temperatures of 90 K. The results indicate that the pulsed laser deposition technique could be used to deposit large‐area films efficiently with adequate substrate movement.

ISSN:0003-6951    

DOI:10.1063/1.103209

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

1‐&mgr;m‐wide Dayem bridges were patterned with a pulsed Xe laser inc‐axis‐oriented YBaCuO films prepared according to the BaF2method. The microbridges have a critical current density of 2×106A/cm2at 77 K, which is typical for an epitaxial film without grain boundaries. When microwave radiation in the centimeter wavelength range is applied, we observe current steps in the current‐voltage characteristic up to 72 K. The dependence of these steps on microwave power is compared with the model of Golovashkin and Lykov {Zh. Eksp. Teor. Fiz.74, 214 (1978) [Sov. Phys. JETP47, 110 (1978)]}; we find that the step amplitude is smaller than predicted.

ISSN:0003-6951    

DOI:10.1063/1.103210

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Superconductor‐normal metal‐superconductor (SNS) Josephson junctions consisting of Y‐Ba‐Cu‐O/Au/Nb film‐layered structure have been fabricated using epitaxial Y‐Ba‐Cu‐O films. SNS junctions witha‐bplane orientated Y‐Ba‐Cu‐O films exhibit the Josephson effect, while the junctions withc‐axis orientated Y‐Ba‐Cu‐O films have no Josephson current. Moreover,a‐bplane orientated junctions show anisotropic Fraunhofer patterns in the magnetic field dependence of the critical current according to the direction of film orientations. These anisotropic behaviors reveal that the proximity effect is strongly affected by the anisotropic coherence length and the magnetic penetration depth of Y‐Ba‐Cu‐O films.

ISSN:0003-6951    

DOI:10.1063/1.103156

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The Y‐Ba‐Cu‐O film prepared by chemical vapor deposition showedTc=91.5 K andBc2(77.3 K)=60 T defined by zero resistance. TheJcvalues measured at 77.3 K were 7.8×105A/cm2atB=0 and 1.0×105A/cm2at 16 T, magnetic fields perpendicular to thecaxis. Small disk‐shaped precipitates possibly regarded as strong flux pinning centers in the Y‐Ba‐Cu‐O films were observed using transmission electron microscopy. The evaluation ofJcrelated to the concentration and configuration of the precipitates was in reasonable agreement with the measuredJcvalues.

ISSN:0003-6951    

DOI:10.1063/1.103211

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Highly oriented Bi‐Sr‐Ca‐Cu‐oxide thin films withTc≥100 K and large (10–20 &mgr;m) grains were used to produce thin‐film dc superconducting quantum interference devices (SQUIDs). The best SQUID, which operated up to 75 K, had an inside loop diameter of ∼18 &mgr;m and an estimated loop inductance of 30 pH. The device was patterned by standard photolithography and had weak links that were likely due to existing grain boundaries around the loop. The effective loop area, calculated from the period of the SQUID modulation, is roughly consistent with the geometrical area of the SQUID loop. Significant hysteresis was observed in the flux‐voltage characteristic which depended on the amplitude of the magnetic field sweep. The 1/fnoise levels measured at 100 Hz in this device gave a flux noiseS&fgr;of 1.0×10−8&Fgr;20/Hz at 4.8 K and 2.3×10−7&Fgr;20/Hz at 60 K. The detailed noise measurements which we report for this SQUID are the first for any Bi‐Sr‐Ca‐Cu‐oxide based SQUID.

ISSN:0003-6951    

DOI:10.1063/1.103157

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

BiPbSrCaCuO films have been deposited for the first time onto polycrystalline CuO substrates by dc sputtering. The films become superconducting after they are post‐annealed in air. Zero resistivity is observed between 38 and 72 K depending on the annealing conditions. The sample showing an onset at 105 K gives an extrapolated zero resistivity at 90 K. The preparation and annealing conditions are described.

ISSN:0003-6951    

DOI:10.1063/1.103212

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The first photoreflectance spectrum from a short‐period strain‐symmetrized SimGensuperlattice has been measured at 87 K. Fifteen electronic transitions were measured between 1.1 and 2.7 eV and fit well to a third derivative functional form. Most of the transition energies were calculated using a one‐band envelope‐function model, adding strain and spin orbit shifts as first‐order corrections. Additional transitions were observed near the expected interband energies in an unstrained Si0.2Ge0.8random alloy. All of the calculated transition energies were found to agree to within 80 meV of the measured values.

ISSN:0003-6951    

DOI:10.1063/1.103158

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have used multielectrode laser diodes to demonstrate a dynamic digital optoelectronic memory with read and write capability. Pulses 5 ns wide are recirculated in the system every 50 ns. Bits may be modified by applying positive or negative voltage control pulses to an intracavity absorber in the device.

ISSN:0003-6951    

DOI:10.1063/1.103159

出版商:AIP    

年代:1990

数据来源: AIP