Heavy fermion material

A strongly correlated material whose low-energy electronic quasiparticles have a very large thermodynamic effective mass. An enhanced electronic heat capacity coefficient, spin susceptibility and quantum-oscillation cyclotron effective mass are complementary signatures; they need not all be related by a single isotropic band mass. A Kondo lattice is an important setting for such behaviour. In CeAl3, low-temperature specific heat and quadratic resistivity provided an early quantitative example.^[ref]

For quasiparticles with density of states $g(E_F)$ including both spins, the leading electronic heat capacity is $C=\gamma T$ with $\gamma ={\pi }^2{k}_B^{2}g(E_F)/3$. A narrow heavy band makes this coefficient large. The density of states and heat capacity must use consistent extensive, molar or volumetric normalization.

The 1975 measurements of CeAl3 below $0.2\mathrm{K}$ found an electronic heat capacity coefficient of $1.62\mathrm{J}\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{K}}^{-2}$ and a quadratic electrical-resistivity coefficient of $35\mu \mathrm{\Omega }\mathrm{cm}{\mathrm{K}}^{-2}$. These are complementary thermal and transport signatures of an unusually dense low-energy electronic spectrum.^[ref] A temperature sweep and a $C/T$ versus $T^2$ fit separate the electronic intercept from a Debye lattice term; the transport comparison tests a Fermi liquid temperature law.