Crossover behavior of the localized to itinerant transition of 5f electrons in the antiferromagnetic Kondo lattice USb2

In uranium-based heavy fermion systems, the 5 f electrons display an intermediate character between partial localization and partial itinerancy, which makes the Kondo problem more complicated. Here we use scanning tunneling microscopy/spectroscopy to investigate the (001) surface of the Kondo lattice antiferromagnet USb2. Temperature-dependent dI/dV spectra from 4.7 K up to 140 K reveal several peak structures around the Fermi level. Two pronounced peaks originate from the hybridization between the conduction and 5 f electrons. We did not observe the mysteriously abrupt change of the electronic state at 45 K, which was previously reported by another scanning tunneling microscopy group and attributed to a novel first-order-like transition. Instead, we only observe continuous evolution of the dI/dV spectra with temperature. Furthermore, in some scanning regions, we find significant Sb atoms missing from the top layer, which gives us the opportunity to investigate the electronic structure of the U-terminated surface. For the U-terminated surface, an additional sharp peak emerges, which is closely related to the magnetic order.