Abstract
In solids containing elements with f orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy fermionic excitations with a heavy effective mass. These excitations are fundamental to the appearance of unconventional superconductivity and non-Fermi-liquid behaviour observed in actinide- and lanthanide-based compounds. Here we use spectroscopic mapping with the scanning tunnelling microscope to detect the emergence of heavy excitations with lowering of temperature in a prototypical family of cerium-based heavy-fermion compounds. We demonstrate the sensitivity of the tunnelling process to the composite nature of these heavy quasiparticles, which arises from quantum entanglement of itinerant conduction and f electrons. Scattering and interference of the composite quasiparticles is used to resolve their energy-momentum structure and to extract their mass enhancement, which develops with decreasing temperature. The lifetime of the emergent heavy quasiparticles reveals signatures of enhanced scattering and their spectral lineshape shows evidence of energy-temperature scaling. These findings demonstrate that proximity to a quantum critical point results in critical damping of the emergent heavy excitation of our Kondo lattice system.
Highlights
In solids containing elements with f orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy fermionic excitations with a heavy effective mass
We demonstrate the sensitivity of the tunnelling process to the composite nature of these heavy quasiparticles, which arises from quantum entanglement of itinerant conduction and f electrons
The lifetime of the emergent heavy quasiparticles reveals signatures of enhanced scattering and their spectral lineshape shows evidence of energy–temperature scaling. These findings demonstrate that proximity to a quantum critical point results in critical damping of the emergent heavy excitation of our Kondo lattice system
Summary
30 60 ordered surfaces of CeCo(In0.9985Hg0.0015)[5]. Following recent theoretical efforts[26,27], we compute spectroscopic properties of a model band structure in which a single hole-like itinerant band of spd-like electrons hybridizes with a narrow band of f-like electrons (see Supplementary Information section I for details of the model). The results of our calculations (Fig. 3c, d) are sensitive to the ratio of tunnelling (tf/tc) into the heavy f states to tunnelling into the light conduction band—a behaviour that explains the differences between the tunnelling processes on the different cleaved surfaces (Fig. 3a, b). Naively one would expect that tunnelling to the heavy excitations would be more pronounced on the Ce–In layer, recent first principles calculations show that the amplitude of the hybridization of the f states with the out-of-plane spd electrons can be remarkably larger than the amplitude of the hybridization with the in-plane spd electrons[21]
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