High-field specific heat of ${\mathrm{CeCu}}_2$${\mathrm{Si}}_2$ and ${\mathrm{CeAl}}_3$

We have measured the low-temperature specific heat, C, of both a superconducting and a nonsuperconducting sample of ${\mathrm{CeCu}}_2$ ${\mathrm{Si}}_2$, as well as a sample of ${\mathrm{CeAl}}_3$, in fields to 23 T. Contrary to all our previous C(H) work on nonsuperconducting Ce-based heavy-fermion systems (HFS’s), the superconducting ${\mathrm{CeCu}}_{2.2}$ ${\mathrm{Si}}_2$ sample has a small response to field, similar to the results for the other heavy-fermion superconductors ${\mathrm{UPt}}_3$ and ${\mathrm{UBe}}_{13}$. Thus, the previous correlation that U-based HFS’s have small changes of C with field and that Ce-based HFS’s have large changes must be discarded. We attempt to correlate other measured properties with our C(H) data for all HFS’s for which such data exist, a total of seven systems, with only limited success. The possibility of a hidden variable linking the lack of large changes in C in 23 T with the occurrence of superconductivity in HFS’s is discussed.