The Crystal Field as a Local Probe in Rare Earth Based High-Temperature Superconductors

Abstract

The discovery of high-temperature superconductivity in the perovskites La2CuO4 [1] and YBa2Cu3O7 [2] has given rise to a large amount of materials research. Of particular importance in determining the nature of the superconductivity is the effect of substituents at various sites in these compounds. It has been realized that the superconducting transition temperature Tc is essentially unchanged upon replacing the Y and La ions by paramagnetic rare-earth (R) ions. This surprising observation is in contrast to conventional superconductors, for which paramagnetic ions usually have a large detrimental effect on superconductivity. It is therefore important to achieve a detailed understanding of the low-energy electronic properties which define the magnetic ground state of the R ions. In particular, information on the crystal-field (CF) interaction at the R site is highly desirable, for the following reasons: (i) For many high-Tc compounds superconductivity and long-range three-dimensional magnetic ordering of the R ion sublattice coexist at low temperatures. An understanding of both the nature of the magnetic ordering and its apparent lack of influence on Tc requires a detailed knowledge of the CF states of the R ions. (ii) There are a few exceptions to the above statement, e.g., Ce and Pr substitution for Y in YBa2Cu3O7 are known to have a drastic detrimental effect on superconductivity. Again, information on the CF states of these particular R ions will help to elucidate the observed loss of superconductivity. KeywordsNuclear Magnetic ResonanceCrystal FieldLocal ProbeCrystal Field ParameterCrystal Field InteractionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.