ABSTRACT
The value of penetration depth is of the order of magnitude of 50 nm for pure metals superconductors. The fundamental phenomena related to the superconductivity may be listed as: zero resistivity, diamagnetic or Meissner effect, energy gap, specific heat discontinuity, magnetic flux quantization, isotopic effect, and tunneling effect. Type II superconductors are all the alloys, intermetallic components and ceramic oxides. For the Type II superconductors the critical density, critical current density corresponds to the current value at which the vortex flow starts to occur. Chemical doping results also in enhancement of flux pinning in novel oxide superconductors. When the energy gap is exceeded, the breaking of electron pairs takes place, leading to the destruction of the superconductivity. An abrupt change of heat capacity is observed during the normal to superconductive transition, which may be explained by the presence of the energy gap.
