CsV₃Sb₅ has attracted growing interest for its unusual crystal structure and complex quantum phenomena. Evidence for time-reversal symmetry breaking remains under debate, and the mechanism of its superconductivity is not fully understood. Studying its response to single-atom impurities provides a way to address these questions.

In a study published in Nature Physics, a team led by Prof. HAO Ning from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences (CAS), along with researchers from Anhui University and the University of Science and Technology of China of CAS, identified two distinct types of unusual low-energy quasiparticle states in the kagome superconductor CsV₃Sb₅ using single-atom impurities as local "quantum probes" combined with scanning tunnelling spectroscopy.

Using an ultralow-temperature, high-magnetic-field scanning tunnelling microscope, the researchers systematically investigated artificially introduced magnetic and non-magnetic impurities, as well as intrinsic vanadium vacancies, in CsV₃Sb₅.

They found that magnetic chromium adatoms produced pronounced Kondo resonance peaks. The spatial pattern of these resonances broke all in-plane mirror symmetries of the kagome lattice—an effect that cannot be explained by conventional charge-density-wave order or electronic nematicity, but aligns with theoretical models involving chiral loop-current order.

In addition, near weakly magnetic vanadium vacancies, the researchers observed a pronounced zero-bias conductance peak within the superconducting gap. This zero-energy mode coexisted with conventional bound states but remained spatially robust and showed behavior close to quantized conductance.

Analysis suggested that this mode arose from local oscillations of the superconducting order parameter induced by magnetic impurities. In the presence of topological surface states, such features may be linked to Majorana zero modes.

The findings of this study offer new insight into defect-induced exotic excitations in topological superconductors.