摘要:

We present a new method to determine the lateral depletion length (LDL) at the boundary of a two‐dimensional electron system (2DES). This approach exploits the fact that in high magnetic fields certain plasma excitations of the confined 2DES (edge‐magnetoplasmons, EMPs) are sensitive to details of the density profile near the edge. Comparing the measured magnetic‐field dispersion of EMPs in a circular mesa with existing classical theories, the LDL is found to be between 0.3 and 0.6 &mgr;m for an electron density of 3.0×1011cm−2. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113189

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Magnetometers based on double relaxation oscillation superconducting quantum interference devices (SQUIDs) (DROSs) have been fabricated and characterized. The DROSs are based on 2×2 &mgr;m2Nb/AlOxtunnel junctions and have a 25 turn, tightly coupled input coil. The high flux‐to‐voltage transfer coefficient of 1–2 mV/&fgr;0facilitates direct voltage readout by a low‐noise dc amplifier. The pickup coil consists of a thin‐film Nb gradiometer with a baseline of 40 mm and an inductance of 110 nH. The white field noise of the magnetometer was better than 5 ft/&sqrt;Hz, which is sufficient for magnetoencephalography measurements. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113190

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Multifilamentary high‐temperature superconductor (HTS) composite conductors have been developed for alternating current (ac) applications. A twisted HTS conductor containing the Bi‐2223 phase fabricated using a modified powder‐in‐tube technique is reported. Transport critical current densities of 13 800 and 10 900 A/cm2(77 K, self‐field, 1 &mgr;V/cm) have been achieved for twisted tape and wire conductors with twist pitches of 3.7 and 3.6 mm, respectively. These conductors are strongly linked and are thus suitable for use in ac applications. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113191

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have developed Josephson junctions and superconducting quantum interference devices (SQUIDs) in a superconductor‐normal‐superconductor edge‐junction design. These devices are unusual in that we use YBa2Cu3O7−xfor both the superconducting and normal layers. The only difference between the layers is the temperature of the substrate during deposition, 695 °C for the superconductor and 670 °C for theNlayer. The lower deposition temperature results in material with a significantly reducedTcand a higher resistivity. The Josephson junctions produced in this fashion haveIcRnproducts typically greater than 100 &mgr;V at 77 K. The SQUIDs are not fully optimized but have produced modulation depths of approximately 10 &mgr;V at 76 K. These SQUID results are similar to the best results in the literature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113192

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Superconductivity withTc&bartil;25–45 K has been induced in films based on the ‘‘infinite layer’’ structure though high temperature annealing in an oxygen ambient. The films had compositions Srn+1CunO2n+1+&dgr;(n=3–9) and were previously grown by laser molecular beam epitaxy by periodic insertion of SrO defect layers into the SrCuO2infinite layer matrix. A marked dependence on the cooling rate at the end of the postgrowth anneals indicates that preservation of a high temperature oxygen sublattice forms the key to enhancing the carrier density in these films, opposite to the situation with YBa2Cu3O7−&dgr; . ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113193

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We studied the response of high‐Tcbiepitaxial grain boundary junctions to 100 GHz radiation in the presence of a magnetic field. Integer as well as subharmonic constant voltage steps are observed, even at one‐fifth of the voltage separation between integer (Shapiro) steps. Our results indicate that this behavior is due to the synchronized motion of Josephson vortices along the junction. We show that this effect is directly related to the width of the junction, and not to an array of weaker regions in the barrier. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113194

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The critical currentIcof YBa2Cu3O7−&dgr;bicrystal grain boundary Josephson junctions (GBJs) have been measured in high magnetic fields up toB=12 T. Even at the highest applied magnetic fields,Icvaried periodically with varying magnetic field. By comparing the envelope of the measuredIc(B) dependencies to model calculations we obtain information on the spatial distribution of the supercurrent densityjcon a length scale down to below 1 nm. Our analysis gives clear evidence thatjchas spatial inhomogeneities on all length scales down to 1 nm with a probability distributionp(a) for the characteristic length scaleaof the inhomogeneities. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113263

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Pulsed‐laser deposition of smooth high‐Tcsuperconducting films almost free from droplets and precipitates with the use of velocity filtration of plasma particles is reported. We have removed droplets from laser‐induced plasma by using a shutter technique; a reduction of the droplet density by a factor of 105has been achieved. We have applied the technique to the preparation of high quality YBa2Cu3O7−&dgr;films on (100)‐oriented SrTiO3, MgO, Y2O3‐stabilized ZrO2(YSZ) substrates and, furthermore, on (11¯02)‐oriented sapphire covered with (100) sublayers of Si and (100) YSZ buffer layers. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113264

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the fabrication and characterization of benzoic acid ion exchanged planar waveguides in lithium tantalate in order to investigate the conditions suitable for achieving quasiphase matching. Samples from az‐cut lithium tantalate wafer were ion exchanged at 205 °C for 3 or 6 h and annealed for between 16 and 120 s at temperatures of between 465 and 594 °C. The anneal diffusion coefficient at a temperature of 525 °C was measured to be 264 &mgr;m2/h. Domain inversion was observed for anneals at 594 °C/30 s and at 594 °C/60 s. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113265

出版商:AIP    

年代:1995

数据来源: AIP