A research team from southern university of science and technology (SUSTech) has uncovered a new way that quantum matter can change its state: a weak magnetic field triggers a transition from a glassy assembly of spin clusters to a coherent heavy-electron metal, in a material where atomic disorder is the rule. The discovery shows that Kondo-breakdown quantum criticality—long theorized but rarely isolated—can occur without long-range magnetic order, expanding the landscape for quantum materials research.
The team studied TiFe x Cu 2x−1 Sb, an off-stoichiometric Heusler-like compound in which Fe and Cu randomly occupy lattice sites, producing strong intrinsic disorder and dilute local magnetic moments. Imaging and spectroscopy reveal the random Fe/Cu distribution, while calculations and magnetization show that only a small fraction of Fe carries sizable moments—placing the system in a dilute Kondo-disordered regime.
At ultra-low temperatures, specific heat and the magnetic Grüneisen parameter follow quantum-critical scaling, pointing to a magnetic-field-induced quantum critical point near 0.13 Tesla.
Transport measurements back up this picture. The resistivity reveals the crossover into coherent Kondo scattering while Hall measurements show a decreasing Hall coefficient with field, consistent with a larger Fermi surface as conduction electrons incorporate localized moments to form composite quasiparticles.
Together, these results demonstrate a Kondo-breakdown route to quantum criticality in a magnetically disordered metal—without long-range magnetic order—and establish TiFe x Cu 2x−1 Sb as a platform for studying strange-metal behavior and emergent many-body phases where disorder and strong correlations intertwine.
National Science Review
Experimental study