Neutron Spectroscopy of Rare Earths in Superconducting Materials

Abstract

Two centuries after the discovery of the rare earths (R) by Lt. C.A Arrhenius (1787) the investigation of the properties of R ions is still an exciting field in solid state physics [1]. The interest in compounds containing rare earths was further enhanced by the discovery of high-temperature superconductivity (HTSC) by Bednorz and Muller [2], because R ions are present in a variety of superconducting (SC) materials. Soon after the first synthesis of the YBa2Cu3O7 substance in 1987 [3,4] it has been realized that Y can be replaced by R ions, except for R=Tb,Ce. In contrast to conventional superconductors, a coexistence of superconductivity (except for R=Pr) and long-range magnetic order of the R sublattice was observed. In the R2-xCexCuO4 materials crystallizing in the T structure superconductivity has been found for R=Pr, Nd, Sm and Eu [5]. In the case of R=Nd and Sm, the R-ions show long-range antiferromagnetic order. The recently discovered quaternary intermetallic superconducting compounds RNi2B2C [6,7] show an interesting interplay between superconductivity and rare earth magnetism, with an almost reentrant behavior into the normal state for R=Ho and to a lesser extent for R=Er and Tm [8,9].