Heavy fermion related behaviors and the effects from nonmagnetic atom vacancies in the $5f$-electron based antiferromagnet $U{\mathrm{As}}_2$

Recent studies on the electronic structures of the $5f$-electron based antiferromagnetic compounds, i.e., uranium dipnictides, have aroused widespread interest in the complex interplay among different channels of interactions, such as Kondo entanglement and antiferromagnetic ordering. Here, we use scanning tunneling microscopy/spectroscopy to explore the complex low-energy excitations in the $5f$-electron based antiferromagnet $U{\mathrm{As}}_2$. The crystal-field excitations are revealed as peaks above the Fermi level in the $dI/dV$ spectra. Temperature-dependent spectroscopic measurements find that Kondo resonance and antiferromagnetic order are manifested as two peaks below the Fermi level, demonstrating that Kondo coherence can be undisturbedly established in the antiferromagnetic phase. The crystal-field excitations, Kondo resonance, and antiferromagnetic state are all locally altered by the presence of As-atom vacancies at the atomic scale and these phenomena prove that the nonmagnetic atom vacancy has a strong influence on low-energy excitations in heavy fermion compounds.