Heavy fermion superconductors are a type of
unconventional superconductor
Unconventional superconductors are materials that display superconductivity which is not explained by the usual BCS theory or its extension, the Eliashberg theory. The pairing in unconventional superconductors may originate from some other mecha ...
.
The first
heavy fermion
In materials science, 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, the ...
superconductor, CeCu
2Si
2, was discovered by
Frank Steglich
Frank Steglich (born 14 March 1941) is a German physicist and the founding director of the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany.
Education and career
Steglich was born in Dresden and studied physics in the Univer ...
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
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 Cooper. ...
s in the superconducting state are also formed by the heavy quasiparticles.
In contrast to normal superconductors it cannot be described by
BCS theory
In physics, the Bardeen–Cooper–Schrieffer (BCS) theory (named after John Bardeen, Leon Cooper, and John Robert Schrieffer) is the first microscopic theory of superconductivity since Heike Kamerlingh Onnes's 1911 discovery. The theory descr ...
. 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
{{Superconductivity
Superconductivity
Correlated electrons
Condensed matter physics