No abstract available

No abstract available

[en] A series of tunneling experiments have been performed on bilayers of tin and lead. Tunneling into the tin side of the proximity effect sandwich the phonon structure of tin is readily observed in d²V/dI² vs V at 4.2 K where tin is a normal metal. The structure is very similar to that observed in tin alone below its transition temperature. In addition there appears some structure from the lead phonons which is strongly dependent on the thickness of the tin film. (author)

[en] Some new, electrically conducting organic compounds show unexpected physical phenomena such as superconductivity, spin-density waves and a novel phase transition induced by an applied magnetic field

No abstract available

[en] We have measured the tunneling characteristics (I, dV/dI, and d²V/dI² vs. voltage) for a series of junctions of the form Al--Ox--Cu--Pb for Cu thicknesses ranging from 400 to 3000 A. From the second derivative characteristics we observe two distinct contributions, one from an electron interference effect and another from the interaction of the superconducting electrons with phonons in the Cu. These contributions may be separated by the application of a magnetic field less than the critical field of the sandwich. The electron interference effect provides a direct measurement of the Fermi velocity in the normal metal, while the interactions with the Cu phonons provide a measurement of the electron--phonon coupling constant. Contamination of the interface between Cu and Pb by oxidation of the Cu allows us to decouple the two films and observe the effects of changing the transmission coefficient t. We find that the electron interference is reduced as t is reduced but its energy dependence is unchanged, so that the evaluation of V/sub F/ is unaffected. The phonon structure from the Cu is also decreased with t. The measured energy gap is proportional to the amplitude of the interference effect, indicating that both measure the pair amplitude at the free surface of the Cu. The phonon structure in Cu is proportional to the induced gap squared, independent of whether the gap is varied by a change in thickness or in transition coefficient. For Cu we find V/sub F/=1.06 x 10⁸ cm/sec and the dimensionless electron--phonon coupling constant lambda=0.11 +- 0.03

[en] The resistivity of NbSe₃ doped with 5% Ta has been measured from room temperature down to 0.5 K and the results compared with similar measurements on pure NbSe₃. The pure sample remains normal to the lowest temperature (0.5 K), whereas the doped sample has a sharp transition to the superconducting state with Tsub(c) = 1.5 +- 0.2 K. Measurements of the critical magnetic field indicate that the Ta doped samples are homogeneous, anisotropic three dimensional superconductors. (author)

[en] The tunneling spectra of Al-oxide-N-S proximity effect junctions show phonon structure not only from the superconducting layer S, but also from the normal metal layer N. We report experimental results for junctions with Ag, Cu, and Al normal metal layers (100--400 A thick) and Pb or Sn superconducting layers (approx.3000 A thick). We compare these experimental results with the McMillan geometrical resonance model of the proximity effect and with an extended McMillan tunneling model. The extension includes the effect of the frequency-dependent electron-phonon interaction in the normal metal. Finally, we estimate the electron-phonon coupling constant lambda for the normal metals from the size of their phonon structure in the tunneling spectra

[en] We have measured the resistance and critical fields of a series of alloys of Ti and Ta substituted for Nb in NbSe₃. For concentrations of 5 at. % Ta and 0.1 at. % Ti we find that the charge-density-wave transitions are greatly smeared or suppressed and that the alloys become bulk anisotropic superconductors. Our results are discussed in terms of the competition between the charge-density waves and superconductivity for states at the Fermi surface

[en] Measurements were made of the critical temperature (Tsub(c)) and the upper critical magnetic field (Hsub(c2)) of Lasub(1-x)Gdsub(x)Ru₂. At low concentrations of the magnetic impurity (Gd), the suppression of Tsub(c) follows the expected Abrikosov-Gorkov (A-G) pair breaking curve. However, for larger concentrations, strong deviations below A-G are observed. Samples in this region (4.< approximately x < approximately 5. at.%) exhibit two Tsub(c)'s. Lasub(1-x)Gdsub(x)Ru₂ is known to order magnetically, probably as a spin glass, and the magnetic ordering temperature (Tsub(M)) has been measured in the normal state. This Tsub(M) curve intersects the Tsub(c) curve in the concentration range where the Tsub(c) is re-entrant and the re-entrant Tsub(c) behavior is therefore attributed to the magnetic ordering of the Gd³⁺ ions. (author)