Resistance Anomalies Accompanying Crossover from Heavy-Fermion Regime to Intermediate-Valence Regime: A Study of Cu–Ni Substitution and Pressure Effects on CeCu2Si2

Abstract

We present detailed investigations on the effects of Ni substitution (x) on Ce(Cu1−xNix)2Si2 with x < 0.3, and a pressure (p) study for x = 0.04(2), 0.05(2), and 0.09(2) by resistivity measurements. The Cu–Ni substitution suppresses both antiferromagnetic fluctuations and superconductivity in CeCu2Si2, and leads to a dramatic crossover from the heavy-fermion (HF) regime to the intermediate-valence (IV) regime with progressive Ni doping. The crossover can be characterized by a marked increase in Kondo temperature evaluated from resistivity, specific heat, and susceptibility measurements. In high-pressure resistivity measurements, the Ni-doped system exhibits similar anomalies to those observed in CeCu2Si2, namely, T-linear dependence, an enhancement of residual resistivity, and a marked decrease in the A coefficient of the T2-resistivity. Furthermore, we observed an unexpected upturn anomaly in resistivity in the Ni-doped system under high pressure. By constructing the x–p phase diagram of Ce(Cu1−xNix)2Si2...