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  • 1
    Digitale Medien
    Digitale Medien
    High-temperature properties of GaInAs/AlGaAs lasers with improved carrier confinement by short-period superlattice quantum well barriers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2863-2865 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The influence of the carrier confinement on the output characteristics of GaInAs/AlGaAs lasers was investigated. To improve the carrier confinement, AlGaAs/GaAs short-period superlattices were used as quantum well barriers. In comparison to lasers with GaAs barriers the structures with the modified barriers show improved temperature properties at low threshold current densities without deterioration of the internal quantum efficiency (〉95%). High characteristic temperatures (T0) well above 300 K were measured between 20 and 75 °C and laser operation up to 238 °C could be achieved. The large improvement in T0 is mainly attributed to the reduced thermionic emission of carriers out of the quantum well due to the increased barrier height and the carrier reflection above the barrier by the short-period superlattice. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.122611
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  • 2
    Digitale Medien
    Digitale Medien
    Magnetic-field-effect three-terminal device based on YBa2Cu3O7−δ grain boundary junctions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1843-1845 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Three-terminal YBa2Cu3O7−δ thin film devices based on a parallel array of grain boundary Josephson junctions were fabricated. The multiloop superconducting device is controlled by the magnetic field generated by a current Ictrl, which modulates the critical current Ic through the Josephson junction array. For these devices a current gain ranging between 2 at 77 K and 5 at 30 K was obtained. The spatial homogeneity of the device properties was studied by low-temperature scanning electron microscopy and by the determination of the supercurrent correlation function. Comparing the measured and the theoretically expected supercurrent correlation function shows that the device characteristics agree well with those expected from the device geometry.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.356326
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  • 3
    Digitale Medien
    Digitale Medien
    Electric field controllable Josephson junctions of high quality in high-Tc superconductors (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3031-3033 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Three-terminal Josephson junctions, the third terminal of which can be used to control the electronic properties of the device, are the key to a number of exciting device applications of high-Tc superconductors. To this end a novel device structure has been developed, which consists of an inverted metal-insulator-superconductor field-effect transistor into which a bicrystal grain boundary junction is embedded. These devices are excellent Josephson junctions as exemplified by their current–voltage characteristics and the magnetic field dependencies of the critical currents. The critical current of the junctions can be changed by 8% per volt applied to the gate electrode, the gate currents being negligible. Because they are sensitive to electric as well as magnetic fields, the junctions can be controlled by two independent inputs. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.115567
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  • 4
    Digitale Medien
    Digitale Medien
    Analysis of the critical current density in grain boundary Josephson junctions on a nanometer scale (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2289-2291 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The critical current Ic of YBa2Cu3O7−δ bicrystal grain boundary Josephson junctions (GBJs) have been measured in high magnetic fields up to B=12 T. Even at the highest applied magnetic fields, Ic varied periodically with varying magnetic field. By comparing the envelope of the measured Ic(B) dependencies to model calculations we obtain information on the spatial distribution of the supercurrent density jc on a length scale down to below 1 nm. Our analysis gives clear evidence that jc has spatial inhomogeneities on all length scales down to 1 nm with a probability distribution p(a) for the characteristic length scale a of the inhomogeneities. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.113263
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  • 5
    Digitale Medien
    Digitale Medien
    Superconducting transport properties of Bi2Sr2CaCu2O8+x bicrystal grain boundary junctions (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 996-998 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have performed a detailed study of the superconducting transport properties of Bi2Sr2CaCu2O8+x bicrystal grain boundary junctions (GBJs). The GBJs were fabricated by the deposition of c-axis oriented epitaxial Bi2Sr2CaCu2O8+x films on SrTiO3 bicrystal substrates. The measured resistive transition R(T), the current-voltage characteristics (IVCs), the temperature dependence of the critical current density Jc(T), and the magnetic field dependence of the critical current Ic(B) of the Bi2Sr2CaCu2O8+x GBJs are similar to those observed for YBa2Cu3O7−δ GBJs. However, for the same misorientation angle the magnitude of Jc is almost an order of magnitude smaller for the BSCCO-GBJs. The R(T) dependencies and the IVCs of the BSCCO-GBJs are close to the prediction of the resistively shunted junction (RSJ) model. The Ic(B) dependencies are close to those of large Josephson junctions with overlap geometry. Our results show that BSCCO-GBJs may be useful for cryoelectronic applications.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.109818
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  • 6
    Digitale Medien
    Digitale Medien
    Magnetic field dependence of the critical current in YBa2Cu3O7−δ bicrystal grain boundary junctions (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 783-785 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have performed a detailed study of the magnetic field dependence of the critical current, Ic(B), of YBa2Cu3O7−δ bicrystal grain boundary junctions (GBJs). GBJs with width W much larger than the Josephson penetration depth λJ show Ic(B) dependencies that are close to those of ideal large Josephson junctions with overlap geometry. The Ic(B) dependencies are symmetrical with respect to B=0 and Ic decreases linearly with increasing applied magnetic field for B≤BJ1, where BJ1 is the lower critical field of the GBJ. Furthermore, Ic(B=0) increases linearly with increasing width of the GBJs as expected for Josephson junctions with overlap geometry. From the measured Ic(B) dependencies the temperature dependence of BJ1 and the London penetration depth could be derived.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.108578
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  • 7
    Digitale Medien
    Digitale Medien
    Distribution of the critical current density and flux trapping in YBa2Cu3O7−δ ramp-edge Josephson junctions (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 241-243 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have studied the spatial distribution of the critical current density in YBa2Cu3O7−δ ramp edge Josephson junctions using low-temperature scanning electron microscopy. Applying this technique allows the imaging of the critical current density distribution with a spatial resolution of about 1 μm. Our measurements show that the geometry of the ramp-edge junction eases the trapping of magnetic flux quanta in the YBa2Cu3O7−δ layer covering the ramp edge. These trapped flux quanta result in a spatially inhomogeneous magnetic field parallel to the barrier layer, which in turn results in a spatially modulated supercurrent density and an unusual magnetic field dependence of the critical current.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.111516
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  • 8
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    Molybdenum isotopic evidence for oxic marine conditions during the latest Permian extinction (2013)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publikationsdatum: 2013-08-09
    Beschreibung: The latest Permian extinction (LPE), ca. 252 Ma, represents the most severe extinction event in Earth’s history. The cause is still debated, but widespread marine anoxic to euxinic (H 2 S rich) conditions, from deep to shallow water environments, are commonly suggested. As a proxy for marine oxygen levels, we analyzed 98/95 Mo of two LPE sections that represent a gradient in water depth on the northwest margin of Pangea. Results from deep-water slope environments show a large shift in 98/95 Mo values from –2.02 to +2.23 at the extinction horizon, consistent with onset of euxinic conditions. In contrast, sub-storm wave base shelf environments show little change in the molybdenum isotopic composition (–1.34 to +0.05), indicating ongoing oxic conditions across the LPE. These results indicate that areas of the continental shelf of northwest Pangea underwent mass extinction under oxic conditions throughout the LPE event, and that shallow-water anoxia was therefore not a global phenomenon.
    Print ISSN: 0091-7613
    Digitale ISSN: 1943-2682
    Thema: Geologie und Paläontologie
    Publiziert von Geological Society of America (GSA)
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