ABSTRACT
Thermodynamic (specific heat, reversible magnetization, tunneling spectroscopy) and transport measurements have been performed on high quality (K,Ba)BiO3 single crystals. The temperature dependence of the magnetic field H(C(p)) corresponding to the onset of the specific heat anomaly presents a clear positive curvature. H(C(p)) is significantly smaller than the field H(Delta) for which the superconducting gap vanishes but is closely related to the irreversibility line deduced from transport data. Moreover, the temperature dependence of the reversible magnetization presents a strong deviation from the Ginzburg-Landau theory emphasizing the peculiar nature of the superconducting transition in this material.
ABSTRACT
Experimental support is found for the multiband model of the superconductivity in the recently discovered system MgB(2) with the transition temperature T(c) = 39 K. By means of Andreev reflection, evidence is obtained for two distinct superconducting energy gaps. The sizes of the two gaps ( Delta(S) = 2.8 meV and Delta(L) = 7 meV) are, respectively, smaller and larger than the expected weak coupling value. Because of the temperature smearing of the spectra the two gaps are hardly distinguishable at elevated temperatures, but when a magnetic field is applied the presence of two gaps can be demonstrated close to the bulk T(c) in the raw data.
ABSTRACT
The interlayer transport in a two-dimensional superconductor can reveal a peak in the temperature as well as the magnetic field dependence of the resistivity near the superconducting transition. The experiment was performed on the highly anisotropic misfit-layer superconductor [(LaSe)(1.14)](NbSe(2)) with T(c) of 1.2 K. The effect is interpreted within the tunneling mechanism of the charge transport across the Josephson-coupled layers via two parallel channels--the quasiparticles and the Cooper pairs. Similar behavior can be found in the high-T(c) cuprates but there it is inevitably interfering with the anomalous normal state. The upper critical magnetic field can be obtained from the interlayer tunneling conductance.