  An explanation of paradoxical behavior of the residual resistivity rho_0 of
the heavy-fermion metal CeCoIn5 in magnetic fields and under pressure is
developed. The source of this behavior is identified as a flattening of the
single-particle spectrum, which exerts profound effects on the specific heat,
thermal expansion coefficient, and magnetic susceptibility in the normal state,
the specific heat jump at the point of superconducting phase transition, and
other properties of strongly correlated electron systems in solids. It is shown
that application of a magnetic field or pressure to a system possessing a flat
band leads to a strong suppression of rho_0. Analysis of its measured
thermodynamic and transport properties yields direct evidence for the presence
of a flat band in CeCoIn5.
