摘要:

We demonstrate a novel piezoelectric-barrier heterostructure designed for efficient all-optical light modulation. The modulation mechanism relies upon drastic photocarrier separation by the piezoelectric field in the barrier layers. We present room temperature results showing that an optical “control” power of 70W/cm2creates in the heart of the structure a space-charge field of about 30 kV/cm, which induces large spectral shifts (≈100 nm) in the photoluminescence spectra of a CdHgTe quantum well in the 1.5 &mgr;m range. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120935

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A Josephson junction has been realized in which the supercurrent flow is regulated by a “normal” control current traversing the normal metal in between the superconducting electrodes. The principle of operation of the devices is based on the existing relation between the magnitude of the supercurrent and the electronic distribution function in the junction. This method for controlling the supercurrent has clear advantages over other known methods and is relevant for superconducting electronics applications. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120612

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have developed a matching scheme for the operation of a rf superconducting quantum interference device (SQUID) with a lumped-element tank circuit at pumping frequencies up to 1 GHz. This conventionalLCresonant circuit is inductively coupled to a matching coil, which is connected to the 50 &OHgr; transmission line. We characterized the flux noise of high-temperature rf SQUIDs at resonant frequencies between 221 and 950 MHz. At about 900 MHz, we obtained the white flux noise of about14.6 &mgr;&fgr;0/Hzwith a SQUID inductanceLS=150 pHand20 &mgr;&fgr;0/HzwithLS=260 pH.Several of such tank circuits can be driven in parallel or in series with only one cable. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120611

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

(Hg1−xRex)Ba2CaCu2Oy(x≈0.1)thin films have been preparedex situonLaAlO3substrates by a two-step process in which anHgO/Re0.1Ba2CaCu2Oymultilayer precursor film is annealed in a quartz tube using an unreacted monoxide pellet containing HgO as an Hg vapor source. By varying the composition of the monoxide pellet, the film orientation can be changed fromc-axis to the predominantlya-axis one. Thea-axis growth of the grains directly on the substrate is confirmed by x-ray diffraction and transmission electron microscopic observation, although the grains are twinned with 90° orientation. Thea-axis films exhibit aTconset andTczero of approximately 110–127 and 55 K, respectively, suggesting substantial influence of weak links at the grain boundaries on their transport properties. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120613

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The magnetic leakage fields from the poles of magnetic nanoparticles down to105–106spins, isolated or situated at the edges of clusters, are observed with Fresnel projection microscopy by the presence of interference fringes generated by the magnetic phase shifts in the imaging electron beam. The particle shapes and localization of fringes are imaged simultaneously with nanometer spatial resolution at∼200 V.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120614

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

By lifting an epitaxial thin film off its growth substrate, we directly and quantitatively demonstrate how elastic strain can alter the magnetic and electrical properties of single-domain epitaxialSrRuO3thin films (1000 Å thick) on vicinal (001)SrTiO3substrates. Free-standing films were then obtained by selective chemical etching of theSrTiO3.X-ray diffraction analysis shows that the free-standing films are strain free, whereas the original as-grown films onSrTiO3substrates are strained due to the lattice mismatch at the growth interface. Relaxation of the lattice strain resulted in a 10 K increase in the Curie temperature to 160 K, and a 20&percent; increase in the saturation magnetic moment to1.45 &mgr;B/Ruatom. Both values for the free-standing films are the same as that of the bulk single crystals. Our results provide direct evidence of the crucial role of the strain effect in determining the properties of the technologically important perovskite epitaxial thin films. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120603

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Single-phasePrBa0.7Sr1.3Cu3O7thin films with the Sr dopant concentration exceeding the solid solubility limit were epitaxially grown on (001)SrTiO3and (001)LaAlO3substrates by pulsed laser deposition (PLD) method. The resistivity of the doped films grown onLaAlO3was significantly lower than that ofPrBa2Cu3O7.For most of the films grown onSrTiO3,the resistivity was higher than that ofPrBa2Cu3O7.The results were explained by considering the Sr-doping effect and lattice-mismatch-induced strain effect. This work shows the potential of PLD to grow single-phase films with the dopant concentration exceeding the solid solubility limit. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120615

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

PolycrystallineCrO2is shown to exhibit a giant magnetoresistance (GMR) at low temperatures. A rapid decrease in the GMR with increasing temperature is correlated with a decrease in the intergranular resistance. Single-crystalCrO2is a half-metallic ferromagnet, as the data are interpreted to reflect two types of charge carriers, crossing a grain boundary: those that tunnel between conduction bands of adjacent grains and those that hop after residing at a localized state for a time long compared to a spin relaxation time. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120616

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A transmission electron microscopy study ofCrN0.6/TiNsuperlattices deposited by reactive magnetron sputtering is described. The stable structure ofCrN0.60is hexagonal, but high resolution transmission electron microscopy images of the superlattices showed thatCrN0.6layers ⩽10 nm thick were cubic, while 50 nm thick layers were hexagonal. That is, the cubic CrN structure was “epitaxially stabilized” by the cubic TiN, with which there is a 2.4&percent; lattice mismatch. The superlattices with hexagonalCrN0.6showed high strains and defect densities within ≈5 nm of each interface, presumably due to the 5.4&percent; volume decrease associated with the cubic-to-hexagonal transformation. The effect of this strain on the transformation is discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120621

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Hydrogen cyanide, formaldehyde, and ammonia are considered important intermediates in amino acid synthesis by electric discharge. In this study, however, amino acid precursors were synthesized from aCO–N2mixture free of hydrogen atoms. An amorphous film composed of carbon, nitrogen, and oxygen was given from a highly activated plasma. When exposed to atmospheric moisture, this film incorporated hydrogen atoms to yield amino acid. This is a mechanism for amino acid synthesis without involving hydrogen cyanide, formaldehyde, and ammonia. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120617

出版商:AIP    

年代:1998

数据来源: AIP