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

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Kondo lattices are typically electrically insulating at low temperatures.
• Recent experiments suggest bulk metallicity exists within the Kondo insulating phase.
• Understanding this metallic signature is crucial for characterizing these complex materials.

Purpose of the Study:

• To visualize the real-space charge landscape of Kondo lattices with atomic resolution.
• To identify the origin of metallic signatures within the insulating phase.
• To investigate the role of defects in heavy-fermion compounds.

Main Methods:

• Utilized scanning tunneling microscopy (STM) for atomic-resolution imaging.
• Examined the heavy-fermion compound uranium ruthenium silicide (URu₂Si₂).
• Investigated the topological Kondo insulator samarium hexaboride (SmB₆).

Main Results:

• Discovered nanometer-scale metallic conduction electron puddles.
• Observed these puddles centered around uranium-site substitutions in URu₂Si₂.
• Found similar metallic puddles around samarium-site defects in SmB₆.
• These defects disturbed the Kondo screening cloud, revealing the metallic parent state.

Conclusions:

• The observed metallic puddles are linked to defects in the Kondo lattice.
• Results suggest these defects may cause the 3D quantum oscillations observed in SmB₆.
• The developed imaging technique offers potential for atomic-scale charge sensing using heavy-fermion probes.