Superconductivity and non-Fermi-liquid behavior in the heavy-fermion compound CeCo$_{1-x}$Ni$_x$In$_5$

TL;DR

This study explores how off-plane Ni impurity affects superconductivity and non-Fermi-liquid behavior in CeCoIn5, revealing impurity-induced quantum criticality and differences in suppression trends among various dopants.

Contribution

It provides new insights into impurity effects on superconductivity and NFL behavior in heavy-fermion compounds, highlighting the role of dopant position and carrier doping.

Findings

Superconducting T_c decreases with Ni doping and vanishes above x=0.25.

NFL behavior emerges at x=0.25, similar to pure CeCoIn5 under magnetic field.

Doping effects on T_c suppression differ among Ni, Sn, and Pt substitutions.

Abstract

The effect of off-plane impurity on superconductivity and non-Fermi-liquid (NFL) behavior in the layered heavy-fermion compound CeCo$_{1-x}$Ni$_x$In$_5$ is investigated by specific heat, magnetization, and electrical resistivity measurements. These measurements reveal that the superconducting (SC) transition temperature T$_c$ monotonically decreases from 2.3 K (x=0) to 0.8 K (x=0.20) with increasing x, and then the SC order disappears above x=0.25. At the same time, the Ni substitution yields the NFL behavior at zero field for x=0.25, characterized by the -ln T divergence in specific heat divided by temperature, C$_p$/T, and magnetic susceptibility, M/B. The NFL behavior in magnetic fields for x=0.25 is quite similar to that seen at around the SC upper critical field in pure CeCoIn$_5$, suggesting that both compounds are governed by the same antiferromagnetic quantum criticality. The resemblance of the doping effect on the SC order among Ni- , Sn-, and Pt-substituted CeCoIn5 supports the argument that the doped carriers are primarily responsible for the breakdown of the SC order. The present investigation further reveals the quantitative differences in the trends of the suppression of superconductivity between Ce(Co,Ni)In$_5$ and the other alloys, such as the rates of decrease in T$_c$, dT$_c$/dx, and specific heat jump at T$_c$, d($\Delta$C$_p$/T$_c$)/dx. We suggest that the occupied positions of the doped ions play an important role in the origin of these differences.