Heavy fermion superconductor

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Heavy fermion superconductors are a type of unconventional superconductor.

The first heavy fermion superconductor, CeCu2Si2, was discovered by Frank Steglich in 1978. [1]

Since then over 30 heavy fermion superconductors were found (in materials based on Ce, U), with a critical temperature up to 2.3 K (in CeCoIn5). [2]

MaterialTC (K)commentsoriginal reference
CeCu2Si20.7first unconventional superconductor [1]
CeCoIn5 2.3highest TC of all Ce-based heavy fermions [2]
CePt3Si0.75first heavy-fermion superconductor with non-centrosymmetric crystal structure [3]
CeIn30.2superconducting only at high pressures [4]
UBe130.85p-wave superconductor [5]
UPt3 0.48several distinct superconducting phases [6]
URu2Si2 1.3mysterious 'hidden-order phase' below 17 K [7]
UPd2Al3 2.0antiferromagnetic below 14 K [8]
UNi2Al31.1antiferromagnetic below 5 K [9]

Heavy fermion materials are intermetallic compounds, containing rare earth or actinide elements. The f-electrons of these atoms hybridize with the normal conduction electrons leading to quasiparticles with an enhanced effective mass.[ citation needed ]

From specific heat measurements one knows that the Cooper pairs in the superconducting state are also formed by the heavy quasiparticles. [10] In contrast to normal superconductors it cannot be described by BCS theory. Due to the large effective mass, [11] the Fermi velocity is reduced and comparable to the inverse Debye frequency. This leads to the failing of the picture of electrons polarizing the lattice as an attractive force.[ citation needed ]

Some heavy fermion superconductors are candidate materials for the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. [12] In particular there has been evidence that CeCoIn5 close to the critical field is in an FFLO state. [13]

Related Research Articles

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CeCoIn5 ("Cerium-Cobalt-Indium 5") is a heavy-fermion superconductor with a layered crystal structure, with somewhat two-dimensional electronic transport properties. The critical temperature of 2.3 K is the highest among all of the Ce-based heavy-fermion superconductors.

UPd2Al3 is a heavy-fermion superconductor with a hexagonal crystal structure and critical temperature Tc=2.0K that was discovered in 1991. 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. Later experiments demonstrated that superconductivity in UPd2Al3 is magnetically mediated, and UPd2Al3 therefore serves as a prime example for non-phonon-mediated superconductors.

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References

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