Heavy Fermion

Heavy Fermion

In solid-state physics, heavy fermion materials are a specific type of intermetallic compound, containing elements with 4f or 5f electrons. Electrons, a kind of fermion, found in such materials are sometimes referred to as heavy electrons. Heavy fermion materials have a low-temperature specific heat whose linear term is up to 1000 times larger than the value expected from the free-electron theory. The properties of the heavy fermion compounds derive from the partly filled f-orbitals of rare earth or actinide ions which behave like localized magnetic moments. The name "heavy fermion" comes from the fact that below a characteristic temperature (typically below 10K) the conduction electrons in these metallic compounds behave as if they had an effective mass up to 1000 times the free-electron mass. This large effective mass is also reflected in a large contribution to the resistivity from electron-electron scattering via the Kadowaki Woods ratio. Heavy fermion behavior has been found in a broad variety of states including metallic, superconducting, insulating and magnetic states. Characteristic examples are CeCu₆, CeAl₃, CeCu₂Si₂, YbAl₃, UBe₁₃ and UPt₃.