The role of quantum criticality in anomalous superconducting order of CeCoIn5 is still unclear because the quantum critical fluctuations are masked by the superconductivity at low magnetic fields. However, the findings on a disappearance of the superconductivity in Ni-doped CeCoIn5 provide a platform to investigate the nature of the quantum critical fluctuations. The magnetization and heat capacity measurements for the Ni-doped alloy reveal anisotropic characteristics of the quantum critical fluctuations. The observed anisotropic properties are quite similar to those seen in the superconducting order of CeCoIn5, especially to the anisotropy in the upper critical field and the Ising-like characteristics in the spin resonance excitation, suggesting a close coupling between the quantum critical fluctuations and the superconductivity.
The article regarding this work:
M. Yokoyama, K. Suzuki, K. Tenya, S. Nakamura, Y. Kono, S. Kittaka, and T. Sakakibara:
"Anisotropic magnetic-field response of quantum critical fluctuations in Ni-doped CeCoIn5",
Physical Review B 99, 054506-1-6 (2019).
link to this paper