摘要:

The interaction ofunbiasedJosephson junction with external electromagnetic field in the presence of externally applied uniform magnetic field is theoretically examined by means of phenomenological treatment. It is proposed that an irradiated junction with suitably chosen parameters shows a bistable behavior of voltage across the junction as a function of the radiation intensity.

ISSN:0021-8979    

DOI:10.1063/1.334438

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The effect of a damping resistance on the relation between a voltageVand a magnetic flux &Fgr; of a dc SQUID is studied theoretically for the case with a large SQUID parameter &bgr;L=2LI0/&Fgr;0, whereLis a loop inductance,I0is a critical current, and &Fgr;0is the flux quantum. An approximate analytical expression for theV‐&Fgr; relation is obtained by replacing the Josephson junctions with ac current generators. It is shown that theV‐&Fgr; relation becomes almost independent of the value of &bgr;Lin the case of large damping. As a result, the conversion efficiencydV/d&Fgr; is not degraded even for large &bgr;L, as is not the case with a conventional SQUID without the damping resistance. This result indicates the possibility to use the SQUID with large &bgr;Lfor the improvement of the coupling between the SQUID and the input coil without the degradation of the conversion efficiency. Effect of the capacitance is also studied. It is shown that the effect of the capacitance becomes remarkable for the case of &bgr;c≳0.4 , where &bgr;cis the McCumber parameter; for example, at &bgr;c=1 the conversion efficiency becomes about 30% of that at &bgr;c=0 . These analytical results are in good agreement with numerical‐simulation ones.

ISSN:0021-8979    

DOI:10.1063/1.334439

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Preparation of high quality Nb/ZrOx/Pb and Nb/TiOx/Pb Josephson tunnel junctions based on single‐crystal niobium thin films is reported.Vmvalues up to 70 mV, as measured at 4.2 K, were obtained as a result of thermal oxidation of the freshly coated surfaces. The specific capacitance of these junctions varies from 0.010–0.022 pF/&mgr;m2, as determined from Fiske modes and the Josephson diffraction patterns. The use of added thermally oxidized metallic coatings on single‐crystal Nb surfaces is shown to modify the tunneling parameters systematically and to offer new possibilities for fabricating all refractory metal Josephson devices.

ISSN:0021-8979    

DOI:10.1063/1.334440

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The reflectivity and wavelength‐modulated reflectivity of Hg1−xCdxTe samples were measured in the 2.0–8.8 eV energy range to determine the dependence of the spectral featuresE1,E1+&Dgr;1,A, andBon composition and on temperature. Spectral features of mechanically polished surfaces and sputter‐etched surfaces were broadened, decreased in magnitude, and shifted to lower energies than those features of Br2‐etched surfaces. At low temperatures, the spectral features of chemically etched surfaces narrow appreciably more than polished or sputter‐etched surfaces, indicating that at room temperature there is a large thermal contribution to the width of the spectral features of chemically etched surfaces.

ISSN:0021-8979    

DOI:10.1063/1.334441

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Model calculations and experiments have been performed to explore the modes of photoacoustic signal generation from highly porous powders. These indicate that two modes of signal generation are important: (i) a thermal mode resulting from heating of the sample and conduction to the transducer gas above the sample, and (ii) a pressure mode resulting from the volumetric expansion of the interstitial gas in the porous sample. For highly porous materials, such as silica, the pressure mode can dominate the photoacoustic signal. Under conditions where the pressure mode is dominant, the frequency dependence of the acoustic magnitude and phase is similar to that of a homogeneous sample in photoacoustic saturation, however, the photoacoustic signal will still scale with absorption coefficient in this regime. The pressure mode of signal generation can be attenuated by compaction of the powdered sample to reduce the porosity. Unambiguous determination of photoacoustic saturation is shown to require measurements as functions of both frequency and porosity. The experimental results show that for highly porous silica even the strongest absorption bands are not in photoacoustic saturation. The results also suggest that infrared light scattering by powders of submicron‐sized particles is not of major significance. This suggests that photoacoustic spectroscopy is extremely well suited to the study of highly porous materials.

ISSN:0021-8979    

DOI:10.1063/1.334442

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Defects responsible for laser damage in visible‐wavelength mirrors are observed at nondamaging intensities using a new video microscope system. Studies suggest that a defect scattering phenomenon combined with lag characteristics of video cameras makes this possible. Properties of the video‐imaged light are described for multilayer dielectric coatings and diamond‐turned metals.

ISSN:0021-8979    

DOI:10.1063/1.334443

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Very stable field electron emission from TiC single crystals was observed. No current fluctuations were included in an emission current of 10 &mgr;A in a vacuum of 10−8Pa. Step‐ and spike‐like current fluctuations were slightly included when the emission current was large. The frequency and the amplitude of the current fluctuations were largely dependent on the sorts of the residual gas molecules. For instance, when the total emission current was 10 &mgr;A, no current fluctuation was included in 10−6Pa of H2; on the other hand, fluctuations of several percents were included in 10−7Pa of O2.

ISSN:0021-8979    

DOI:10.1063/1.334444

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We show that it is possible to construct a quantum‐limited gravitational wave antenna if it is operated at 0.05 K. We assume a dc SQUID readout of a Paik transducer. We take account of the correlations between the SQUID voltage and current noise and the SQUID dynamic impedance. We derive expressions for the back action of the SQUID on the antenna, for the noise properties of the system, and the sensitivity and matching conditions.

ISSN:0021-8979    

DOI:10.1063/1.334445

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

High‐pressure studies on high quality AlxGa1−xAs double heterostructure light emitting diodes (LEDs) grown by liquid phase epitaxy (LPE) are presented. The AlxGa1−xAs active region varies in composition fromx∼0.25 tox∼0.53, i.e., through the important region of the direct‐indirect crossover (x≡xc≊0.45). The pressure coefficient of the &Ggr; conduction band is observed to decrease (∼1 meV/kbar forx∼0.25 tox∼0.53) with increasing Al concentration, which is in accord with alloy disorder and band‐edge bowing. Indirect‐gap (X) recombination radiation of significant intensity is observed and provides evidence for the high quality of the LPE diodes. High‐pressure measurements, and the corresponding increase in energy of the direct band edge and decrease in the indirect band edge, show that the light emission is a strong function of the carrier distribution in the &Ggr; andXconduction‐band minima. Comparison LEDs fabricated from a crystal (x∼0.37) grown by metalorganic chemical vapor deposition exhibit nearly similar behavior as the LPE LEDs with application of pressure but with an order of magnitude lower light emission.

ISSN:0021-8979    

DOI:10.1063/1.334446

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The infinitesimal stability of fluid vesicle shapes is studied as a function of vesicle volume and spontaneous membrane curvature at fixed area. It is found that the azimuthally symmetric shapes are infinitesimally unstable for some values of these parameters. A possible connection with the sickling of red blood cells is pointed out.

ISSN:0021-8979    

DOI:10.1063/1.334447

出版商:AIP    

年代:1985

数据来源: AIP