Transport Properties of Heavy Fermion Compounds: YbIn1−xCu4+x and YbIn1−yAgyCu4

The iIntermetallic compounds of Yb with In and Cu (YbIn1−xCu4+x) and Yb with In, Ag, and Cu (YbIn1−yAgyCu4) exhibit iInteresting magnetic and transport properties. Of the compounds of Yb with In and Cu the compound with x=0, namely YbInCu4 , has attracted particular attention, because—while being a Curie–Weiss paramagnet—it undergoes a first-order isostructural phase transition at Tv=approx. 40 to 80 K and atmospheric pressure. Below Tv the ytterbium in this compound is in a mixed-valence state and the compound as a whole is sometimes called a light heavy-fermion system. Above Tv , the compound is known as a Curie–Weiss paramagnet of localized magnetic moments and, below Tv , a Pauli paramagnet in a nonmagnetic Fermi-liquid state. In the present paper the results of measurements of the thermal conductivity of polycrystalline samples, YbIn1−xCu4+x with x=0,0.015, 0.095, and 0.17 and YbIn1−yAgyCu4 with y=0, 0.3, 0.7, and 1.0, are reported. The thermal conductivity is separated into the phonon thermal conductivity (oph) (i.e., related to the heat carried by phonons) and into the electronic thermal conductivity (oe) (related to the heat carried by electrons). The electrical resistivity of the compounds was measured to determine the temperature dependence of the Lorenz