Visualizing heavy fermions emerging in a quantum critical Kondo lattice

Area of Science:

• Condensed Matter Physics
• Quantum Materials Science

Background:

• Solids with f orbitals exhibit interactions between f-electron spins and itinerant electrons.
• This interaction forms low-energy fermionic excitations with heavy effective mass, crucial for unconventional superconductivity and non-Fermi-liquid behavior in actinide and lanthanide compounds.

Purpose of the Study:

• To spectroscopically map the emergence of heavy excitations in cerium-based heavy-fermion compounds.
• To demonstrate the sensitivity of tunnelling spectroscopy to the composite nature of heavy quasiparticles.

Main Methods:

• Spectroscopic mapping using scanning tunnelling microscopy (STM).
• Analysis of quasiparticle scattering and interference to determine energy-momentum structure and mass enhancement.
• Investigating quasiparticle lifetime and spectral lineshape for temperature scaling.

Main Results:

• Observed the emergence of heavy excitations with decreasing temperature in cerium-based compounds.
• Demonstrated that tunnelling is sensitive to the quantum entanglement forming these composite quasiparticles.
• Extracted mass enhancement and observed energy-temperature scaling in spectral lineshapes, indicating proximity to a quantum critical point.

Conclusions:

• Proximity to a quantum critical point leads to critical damping of emergent heavy excitations in Kondo lattice systems.
• Scanning tunnelling microscopy is a powerful tool for resolving the energy-momentum structure and composite nature of heavy quasiparticles.
• Findings provide fundamental insights into the mechanisms driving unconventional superconductivity and non-Fermi-liquid behavior.