Observation of the d-wave Kondo Effect

The Kondo effect, one of the most fundamental interactions, underlies a wide range of strongly correlated phenomena, including unconventional superconductivity, quantum criticality, and non-Fermi liquid behavior. Understanding its manifestation in solids has mostly been based on a prototypical Kondo lattice model, in which hybridization between local moments and conduction electrons leads to an isotropic Kondo gap at low temperatures. While the symmetry classification of quantum states, such as the d-wave superconductivity and d-wave magnetic states (e.g. altermagnetism), is well established, an unconventional d-wave Kondo gap has not been experimentally observed. In this article, we employ scanning tunneling microscopy to investigate a quasi-two-dimensional van der Waals actinide, UOTe, and use quasi-particle interference to image the dispersion of the Kondo flat bands. We observe, for the first time, a d-wave Kondo gap. Our theoretical analysis shows that this d-wave Kondo gap arises from the distinct symmetry representations of the Kondo flat band and the dispersive bands. This work presents the first experimental approach for accessing the symmetry properties of Kondo flat bands, a key component in determining their topological character.