Heavy fermion superconductors are a type of
unconventional superconductor
Unconventional superconductors are materials that display superconductivity which does not conform to either the conventional BCS theory or Nikolay Bogolyubov's theory or its extensions.
History
The superconducting properties of CeCu2Si2, a ty ...
.
The first
heavy fermion
In solid-state physics, heavy fermion materials are a specific type of intermetallic compound, containing elements with 4f or 5f electrons in unfilled electron bands. Electrons are one type of fermion, and when they are found in such materials, th ...
superconductor, CeCu
2Si
2, was discovered by
Frank Steglich
Frank Steglich (born 14 March 1941) is a German physicist.
He studied physics in the University of Münster and the University of Göttingen. He received the Gottfried Wilhelm Leibniz Prize by the Deutsche Forschungsgemeinschaft in 1986 and a num ...
in 1978.
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 CeCoIn
5).
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.
From specific heat measurements (ΔC/C(T
C) one knows that the
Cooper pair
In condensed matter physics, a Cooper pair or BCS pair (Bardeen–Cooper–Schrieffer pair) is a pair of electrons (or other fermions) bound together at low temperatures in a certain manner first described in 1956 by American physicist Leon Coope ...
s in the superconducting state are also formed by the heavy quasiparticles.
In contrast to normal superconductors it cannot be described by BCS-Theory. Due to the large effective mass, 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.
Some heavy fermion superconductors are candidate materials for the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. In particular there has been evidence that CeCoIn
5 close to the critical field is in an FFLO state.
References
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Superconductivity
Correlated electrons
Condensed matter physics