Cross-over behavior of the localized to itinerant transition of 5f electrons in the antiferromagnetic Kondo lattice USb2

TL;DR

This study uses STM/STS to explore the temperature-dependent electronic structure of USb2, revealing a continuous evolution of hybridization features and magnetic-related peaks, challenging previous reports of abrupt electronic transitions.

Contribution

It provides new insights into the crossover behavior of 5f electrons in USb2, showing a smooth transition rather than a first-order change at 45 K.

Findings

Continuous evolution of dI/dV spectra with temperature

Identification of hybridization peaks near the Fermi level

Emergence of a magnetic-related peak on U-terminated surface

Abstract

In Uranium-based heavy fermion system, the 5f 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 are originated from the hybridization between the conduction and 5f electrons. We did not observe the mysteriously abrupt change of the electronic state at 45 K, which is previously reported by another STM 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.