Quantum criticality linked to the suppressed superconducting upper critical field in Ni-doped CeCoIn5

Abstract

We demonstrate a close connection between the quantum critical point (QCP) and superconducting upper critical field $H_{c2}$ in the Ni-doped heavy-fermion superconductor ${\mathrm{CeCoIn}}_5$. Temperature variations of electrical resistivity $\rho \left(T\right)$ exhibit a crossover between the non-Fermi liquid and the Fermi liquid states, whose boundary for $T\to 0$, regarded as the QCP, coincides with $H_{c2}$, while $H_{c2}$ decreases to zero with increasing Ni concentrations up to 25%. Furthermore, the $A$ coefficient of the $T^2$ term in $\rho \left(T\right)$ estimated in the Fermi liquid region shows the diverging behavior with decreasing the magnetic field $H$ toward $H_{c2}$. These experimental results suggest that the emergence of the QCP is always accompanied by the breakdown of the superconducting state by $H$ in Ni-doped ${\mathrm{CeCoIn}}_5$.