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.
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We acknowledge discussions with P. W. Anderson, E. Abrahams, P. Coleman, N. Curro, D. Pines, D. Morr, T. Senthil, S. Sachdev, M. Vojta, C. Varma and C. V. Parker. Work at Princeton University was primarily supported by a grant from the DOE Office of Basic Energy Sciences (DE-FG02-07ER46419). The instrumentation and infrastructure at the Princeton Nanoscale Microscopy Laboratory are also supported by grants from the NSF-DMR1104612 and NSF-MRSEC programmes through the Princeton Center for Complex Materials (DMR-0819860), and the W.M. Keck foundation as well as the Eric and Linda Schmidt Transformative fund at Princeton. P.A. acknowledges postdoctoral fellowship support through the Princeton Center for Complex Materials funded by the NSF-MRSEC programme. Work at Los Alamos National Laboratory was performed under the auspices of the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering. Z.F. acknowledges support from NSF-DMR-0801253.
The authors declare no competing financial interests.
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Aynajian, P., da Silva Neto, E., Gyenis, A. et al. Visualizing heavy fermions emerging in a quantum critical Kondo lattice. Nature 486, 201–206 (2012). https://doi.org/10.1038/nature11204
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