UPd2Al3
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UPd2Al3 is a heavy-fermion superconductor with a hexagonal crystal structure and critical temperature Tc=2.0K that was discovered in 1991.[1] Furthermore, UPd2Al3 orders antiferromagnetically at TN=14K, and UPd2Al3 thus features the unusual behavior that this material, at temperatures below 2K, is simultaneously superconducting and magnetically ordered.[2] Later experiments demonstrated that superconductivity in UPd2Al3 is magnetically mediated,[3] and UPd2Al3 therefore serves as a prime example for non-phonon-mediated superconductors.
Heavy-fermion superconductivity was discovered already in the late 1970s (with CeCu2Si2 being the first example), but the number of heavy-fermion compounds known to superconduct was still very small in the early 1990s, when Christoph Geibel in the group of Frank Steglich found two closely related heavy-fermion superconductors, UNi2Al3 (Tc=1K) and UPd2Al3 (Tc=2K), which were published in 1991.[4][1] At that point, the Tc=2.0K of UPd2Al3 was the highest critical temperature amongst all known heavy-fermion superconductors, and this record would stand for 10 years until CeCoIn5 was discovered in 2001.[5]