The Kondo lattice in 1T-TaSSe single crystal as revealed by mK-STM

The Kondo effect arises from the exchange interaction between a localized magnetic moment and conduction electrons, leading to electron scattering and manifesting as a resonance feature in dI/dV in scanning tunneling microscopy (STM) measurements. The 1T-TaS_2-xSe_x system is a promising candidate for observing the Kondo resonance, as it features a Star-of-David charge density wave (CDW) phase, which can create localized spins, as well as superconductivity when the Se doping level approaches 1. The Kondo effect has previously been reported in heterostructures of 1T/1H-TaS₂ and 1T/1H-TaSe₂, as well as in Pb intercalated 1T-TaS₂. Here we investigate 1T-TaSSe single crystals at 40mK using STM after in-situ cleaving the samples in ultra-high vacuum. Each Star-of-David exhibits a Kondo resonance with distinct Fano line shape, which remains unchanged within the Star-of-David clusters, suggesting an orbital origin for the Fano line shape. The splitting of the Kondo resonance peak has also been confirmed in the presence of either in-plane or out-of-plane magnetic fields. The further understanding of the coexistence of superconductivity and Kondo resonance in 1T-TaSSe will provide insights into the interplay between these two competing phenomena.