SUBSTITUTIONS IN YBA2CU3O7-GAMMA AND THEIR INFLUENCE ON THE MAGNETIC PENETRATION DEPTH, ITS ANISOTROPY AND T-C - MUON SPIN ROTATION (MU-SR)

Deterioration of the superconducting properties of HTC materials, induced by different substitutions, offers a key towards the understanding of the basic HTC interactions. Similar effects are obtained either by doping of layers of the perovskite not directly involved in the superconducting mechanism, or by direct substitution of the copper itself. However, this apparent similarity is misleading. In YBCO, for instance, in the first case the oxygen content or the substitution of Y with Pr4+ appear to control essentially the carrier density, n, while in the second case the direct substitution of Cu in the bilayers by Zn or Ni affects more extensively the overall electronic structure of the material. A sensitive experimental tool, such as mu SR, detects correspondingly different behaviours.