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. Here we visualize the real-space charge landscape within a Kondo lattice with atomic resolution using a scanning tunneling microscope. We discover nanometer-scale puddles of metallic conduction electrons centered around uranium-site substitutions in the heavy-fermion compound URu2Si2, and around samarium-site defects in the topological Kondo insulator SmB6. These defects disturb the Kondo screening cloud, leaving behind a fingerprint of the metallic parent state. Our results suggest that the mysterious 3D quantum oscillations measured in SmB6 could arise from these Kondo-lattice defects, although we cannot rule out other explanations. Our imaging technique could enable the development of atomic-scale charge sensors using heavy-fermion probes.
@article{arxiv.2303.15432,
title = {Visualizing the atomic-scale origin of metallic behavior in Kondo insulators},
author = {Harris Pirie and Eric Mascot and Christian E. Matt and Yu Liu and Pengcheng Chen and M. H. Hamidian and Shanta Saha and Xiangfeng Wang and Johnpierre Paglione and Graeme Luke and David Goldhaber-Gordon and Cyrus F. Hirjibehedin and J. C. Séamus Davis and Dirk K. Morr and Jennifer E. Hoffman},
journal= {arXiv preprint arXiv:2303.15432},
year = {2023}
}