Dispersion of first excited crystal field in CeIn₃

Heavy fermion materials are characterized by strong correlations of itinerant and localized electrons. Cerium-based heavy fermion magnets are a particularly interesting subset of this material class, considered the prototypical example of quantum critical phase transitions, among other novel properties. The large spread in energy scales makes first-principles based theoretical modeling of these systems difficult. However, recently, agreement was reached between experiment and theory for the low energy magnons in CeIn₃ [1]. Motivated by this success, this theoretical protocol was extended to include excited crystal field (CEF) states in the material. Here, we discuss the inelastic neutron signal of CeIn₃ at T = 5 K measured with time-of-flight neutron spectroscopy capable of accessing the first excited CEF level. We find that the width of the first excited CEF is broad--to the point that it overlaps with the low-energy magnon at certain points in the Brillouin zone. We further compare the dispersion of the excited CEF level with our theoretical prediction. These results provide insight into the microscopic origin of the low energy physics of heavy fermion materials.

[1] W. Simeth, et al., Nat Commun 14, 8239 (2023).