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]
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 Δ Δ --> C / C ( T C ) {\displaystyle \Delta C/C(T_{\rm {C}})} 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]
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