Onset of superconductivity

Fig. 9. Resistivity versus temperature showing onset of superconductivity for a single crystal (-) and for two highly oriented films (—), where...

Figure 4 Diffraction patterns (Bragg-Brentano geometry) of three superconducting thin Aims ( 2- im thick) anneaied for different times. The temperatures for 0 resistance and for the onset of superconductivity are noted.

Paul" Chu, and others at University of Houston, also reproduced Zurich s I.B.M. research results (156). Bell Lab s confirmation of Bednorz and Muller s discovery of high Tc superconductivity in copper oxide compounds was published (157) in the Jan. 1987 issue of Physical Review Letters. The electrical resistivity data from their work showing an onset of superconductivity at 36.5 K for the composition Lax gSr0 2Cu04 is plotted as Figure 28. This product also showed a 60-70% Meissner effect. 

In agreement with the overall behaviour of the / Ni2B2C compounds with heavy 4f elements R, shown in fig. g, this compound is the unique member of the / Ni2B2C series in which the onset of superconductivity takes place in an antiferromagnetically ordered state i.e. jTn — 11 K>7 C = 6.3K (also see table 7). It should be noted that in the ruthenocuprates discussed in subsection 1.3 also antiferromagnetic order (and even... 

Also the experimental indications on the essential role of the interband electron-phonon coupling, which follows from the investigation of phonon frequency anomalies at the onset of superconductivity must be mentioned [38]. 

Within the theory presented here, the onset of superconductivity, Tc, is when the condition, v = co, takes place. At this point, the normal conduction through free-electrons becomes zero and therefore is frozen . As stated before, the phonon (antisymmetric normal mode) vibration is written as ... 

K and 3.6 K, respectively). The diamagnetic signal of Ba4C60 disappears upon doping with K, with two onsets of superconductivity being displayed. The one at... 

In conclusion, we have shown that according to the doping level in Bi-2212, the onset of superconductivity is associated with a decrease of kinetic energy in the underdoped material, whereas the overdoped material exhibits an increase of kinetic energy. Such a drastic difference confirms that the superconducting state in the underdoped regime of cuprates is unconventional. 

Table 1. Superconducting properties of the samples label, nominal composition, lattice constants a and c, onset of superconducting transition as measured by susceptibility (1-3) or deduced from lattice parameters6 (4-5), isotropic shift CT so and fidl width at half maximum A...

The physical origin of this zero-frequency collective mode is not yet clarified. Two possible mechanisms could be considered (1) the onset of superconducting fluctuations below 30 K, and (2) the contribution of sliding... 

The synthesis of macroscopic amounts of C o and C70 (fullerenes) has stimuiated a variety of studies on their chemical and physical properties. We recently demonstrated that C o and C70 become conductive when doped with alkali metals. Here we describe iow-temperature studies of potassium-doped both as films and bulk samples, and demonstrate that this material becomes superconducting, Superconductivity is demonstrated by microwave, resistivity and Melssner-effect measurements. Both polycrystalline powders and thin-flim samples were studied. A thin film showed a resistance transition with an onset temperature of 16 K and essentially zero resistance near 5 K. Bulk samples showed a well-defined Meissner effect and magnetic-field-dependent microwave absorption beginning at 18 K. The onset of superconductivity at 18 K is the highest yet observed for a molecular superconductor. 

Being able to conduct diffraction studies at different temperatures is important when correlations between structural changes and other temperature-dependent physical properties are to be studied. Examples include the study of structures that undergo phase transitions. These may be structural phase transitions or other types of transitions such as magnetic order/disorder or onset of superconductivity transitions. 

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