Scanning SQUID Study of the Interplay between Superconductivity and Antiferromagnetism: CeCo(In_1-xZn_x)₅

CeCo(In_1-xZn_x)₅ offers a unique platform for exploring the interplay between superconductivity and antiferromagnetism, as well as quantum critical phenomena. Doping non-magnetic Zn atoms at the In site suppresses the Kondo screening effect, leading to the emergence of antiferromagnetic order. The Néel temperature (T_N) increases with Zn concentration (x), while the superconducting critical temperature (T_c) decreases. However, superconductivity and antiferromagnetic order coexist above x ~ 0.03. Recent muon spin relaxation measurements revealed that the penetration depth at zero temperature diverges near the quantum critical point at x ~ 0.03.

To investigate the microscopic nature of the interplay between superconductivity and antiferromagnetism, we measured the local magnetic susceptibility and imaged the magnetic fields of isolated vortices in CeCo(In_1-xZn_x)₅ (x = 0, 0.03, 0.045, 0.06) using scanning superconducting quantum interference device (SQUID) susceptometer. We observed the temperature dependence of the penetration depth, which followed a power law, Tⁿ. The exponent n approaches 2 from 1.5 as Zn concentration increases, consistent with the non-magnetic impurity scattering scenario in a d-wave superconductor. At x = 0.06, near T_N, the paramagnetic susceptibility dropped toward zero without exhibiting a peak structure. This absence of a peak around T_N suggests an inhomogeneous antiferromagnetic order, consistent with previous nuclear magnetic resonance results.

In this presentation, we will present additional data from other samples and further discuss the detailed interplay between superconductivity and antiferromagnetism in CeCo(In_1-xZn_x)₅.