Abstract
Since the discovery by Steglich et al. (1979) of superconductivity in the high-effective-mass () electrons in Ce, the search for and characterization of such "heavy-fermion" systems has been a rapidly growing field of study. The eight heavy-fermion systems known to date include superconductors (Ce, U, U), magnets (Np, , U), and materials in which no ordering is observed (Ce, Ce). These -electron materials have, in comparison to normal metals, enormous specific heat values (450-1600 mJ/mol ), large values of the low-temperature magnetic susceptibility (8-50× emu/mol G), maxima in the resistivity at low temperatures with large values (100-200 μΩ cm), and unusual temperature dependences of their specific heats below 10 K. The three heavy-fermion superconductors show such unusual behavior that the possibility of -wave pairing of the superconducting electrons, rather than the usual BCS -wave pairing, cannot be ruled out. This paper reviews the experimental results to date, to serve both as a status report and as a starting point for future research. Several correlations between properties are pointed out, including the observation that a low value of the Wilson ratio () appears to correlate with the occurrence of superconductivity.
DOI:https://doi.org/10.1103/RevModPhys.56.755
©1984 American Physical Society