[Paper] Revealing magnetic quantum criticality through local superconducting measurements

Our work on magnetic quantum criticality in Zn-doped CeCoIn$_5$ was published in Physical Review Letters on August 26, 2026.

Quantum critical behavior in chemically tuned superconductors is often obscured by spatial variations in dopant concentration. In this work, we developed a local approach that combines scanning SQUID measurements of the magnetic penetration depth with spatial mapping of the superconducting transition temperature, $T_{\mathrm c}$, in Zn-doped CeCoIn$_5$.

Rather than organizing the data by nominal Zn concentration, we used the locally measured $T_{\mathrm c}$ as an effective tuning parameter. This substantially reduces the ambiguity caused by chemical inhomogeneity and allows penetration depth measurements from different microscopic regions and samples to be compared on a common local basis.

Using this approach, we resolved a pronounced peak in the zero-temperature penetration depth near the antiferromagnetic quantum critical point. The result differs substantially from the behavior inferred from macroscopic averaging and cannot be explained by impurity scattering alone. Instead, it is consistent with a disorder-modified quantum critical regime in which magnetic correlations strongly suppress the superconducting superfluid stiffness.

More broadly, this work establishes local $T_{\mathrm c}$ mapping combined with local penetration depth measurements as a general strategy for studying quantum criticality in intrinsically inhomogeneous superconductors.

Magnetic quantum criticality inside the superconducting state revealed by penetration depth scaling with local $T_{\mathrm c}$
Yusuke Iguchi, Kaede Inoh, Ryosuke Koizumi, and Makoto Yokoyama
Physical Review Letters 137, 096001 (2026)
preprint (arXiv:2604.27507)