Second heavy‐fermion superconductor

The recent demonstration of superconductivity in uranium beryllide $({\mathrm{UBe}}_{13})$ by an ETH–Los Alamos collaboration provides us the second example of an exotic and potentially instructive new class of materials, the “heavy‐fermion superconductors.” Four years ago, Frank Steglich and his colleagues at Darmstadt and Cologne reported the discovery of the first of these unconventional and somewhat puzzling new superconductors—${\mathrm{CeCu}}_2{\mathrm{Si}}_2.$ The unearthing of ${\mathrm{UBe}}_{13}$ is important not only because it shows that ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ is not a unique abberation. Until recently, investigations of ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ have been plagued by the difficulty of fabricating stoichiometrically clean, reproducible samples of this material; different samples were giving distressingly different results. With the advent of ${\mathrm{UBe}}_{13},$ where one does not have this metallurgical problem, and with new techniques for making crystalline ${\mathrm{CeCu}}_2{\mathrm{Si}}_2$ samples of high quality, one now has two sources of reliable data on the heavy‐fermion superconductors.