= Solution
In a <heavy fermion material>, correlated low-energy quasiparticles have a large electronic density of states and effective mass. A <Kondo lattice> with hybridization between localized f-electron states and conduction states is an important setting. The large mass is a low-energy dynamical property, not a change in the electron's bare mass or the ionic mass.
Low-temperature calorimetry measures $C/T\simeq\gamma+\beta T^2$ in a regime where an electronic linear term and a Debye lattice term are appropriate. The large intercept $\gamma=(\pi^2k_B^2/3)D(E_F)$ measures the enhanced quasiparticle density of states, with volume or molar conventions kept consistent. Apply a known heat pulse to a thermally characterized sample platform and measure the temperature rise, then vary the base temperature to separate contributions.
In <low-temperature calorimetry and resistivity of CeAl3>, measurements below $0.2\,\mathrm K$ gave $\gamma=1.62\,\mathrm{J\,mol^{-1}\,K^{-2}}$ and $\rho=\rho_0+AT^2$ with $A=35\,\mu\Omega\,\mathrm{cm\,K^{-2}}$. The large thermal coefficient and enhanced quadratic transport coefficient are complementary evidence for a strongly renormalized <Fermi liquid>.<4f-Virtual-Bound-State Formation in CeAl3 at Low Temperatures by Klaus Andres and others>[Abstract: measured coefficients and sub-0.2 K range]{ref} Enhanced spin susceptibility provides another probe. Where coherent quantum oscillations can be resolved, their thermal damping determines a <cyclotron effective mass>, giving a band-sensitive comparison with the thermodynamic mass inferred from heat capacity.
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