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 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.

Published Article - Science 379, 1214-1218 - March 2023

How Kondo-holes create intense nanoscale heavy-fermion hybridization disorder

Electronic structure of Kondo holes in the Th-doped heavy Fermion compound URu₂Si₂ is visualized with STM to find heterogeneous hybridization strength in nanoscale.

Published Article - Proc. Nat'l Acad. Sci. 108, 18233 - Nov 2011