Visualizing the atomic-scale origin of metallic behavior in Kondo insulators

A Kondo lattice is often electrically insulating at low temperatures. However, several recent experiments have detected signatures of bulk metallicity within this Kondo insulating phase. In this study, we visualized the real-space charge landscape within a Kondo lattice with atomic resolution using a scanning tunneling microscope. We discovered nanometer-scale puddles of metallic conduction electrons centered around uranium-site substitutions in the heavy-fermion compound uranium ruthenium silicide (URu2Si2) and around samarium-site defects in the topological Kondo insulator samarium hexaboride (SmB6). These defects disturbed the Kondo screening cloud, leaving behind a fingerprint of the metallic parent state. Our results suggest that the three-dimensional quantum oscillations measured in SmB6 arise from Kondo-lattice defects, although we cannot exclude other explanations. Our imaging technique could enable the development of atomic-scale charge sensors using heavy-fermion probes.

Automated summary

In this study, we used a scanning tunneling microscope to visualize the real-space charge landscape of a Kondo lattice. We observed nanometer-scale puddles of metallic conduction electrons around uranium-site substitutions in URu2Si2 and around samarium-site defects in SmB6. These defects disrupted the Kondo screening cloud and revealed the metallic parent state. This research suggests that the three-dimensional quantum oscillations observed in SmB6 may arise from Kondo-lattice defects.