Metal-insulator transition in the amorphous Ce_xSi_100-x (4 ≤ x ≤ 83) heavy fermion system

The electronic structure, magnetic properties and electron transport properties have been studied on amorphous Ce_xSi_100-x (4 ≤ x ≤ 83) alloys in comparison with non-magnetic amorphous La_xSi_100-x (11 ≤x ≤ 63) and Ti_xSi_100-x (6 ≤ x ≤ 41) alloys with a particular emphasis on the formation of the pseudogap at the Fermi level and its effect on the electron transport upon approaching the metal-insulator transition in the heavy fermion system. It is shown that the interaction between conduction electrons and localized moments leads to an anomalous enhancement in the temperature dependence of the measured resistivity below 10 K. We also revealed that the amorphous Ce_xSi_100-x alloy system crosses the metal-insulator transition at about 12 at%Ce and that the marginally metallic Ce₁₅Si₈₅ alloy has the resistivity of 1500 μΩcm comparable to those in the non-magnetic reference syste ms but a large electronic specific heat coefficient γ of 22 mJ/mol.K², which is 50 times as large as the value of 0.4 mJ/mol.K² for the marginally metallic Ti₁₃ Si₈₇ alloy. The set of (ρ₃₀₀ K, γ_exp) data fall on an extremely small diffusion constant line in the ρ-γ diagram. This unique behavior is attributed to the existence of Ce-4f electrons at the Fermi level, which give rise to a large value of γ but are localized and immobile even in the metallic regime.