Evidence for correlation effects in noncentrosymmetric type II Weyl semimetals
The interplay of topology with electronic correlations has been explored only recently and is acquiring increasing interest in the on-going solid state physics research, since it leads to concepts of paramount importance for the understanding of innovative functionalities in quantum materials.
The family of the noncentrosymmetric RAlGe (R = rare earth) materials is a suitable arena in order to advance our knowledge on novel topological states which cover all varieties of Weyl semimetals, inversion and time-reversal breaking symmetry, depending on a suitable choice of the R element.
Our work presents measurements of the optical reflectivity, collected from the far-infrared to the ultraviolet at nearly normal incidence as a function of temperature. This is the prerequisite in order to perform reliable Kramers-Kronig transformation of the measured quantity, giving access to all optical functions. A dedicated analysis with theoretically based tools allows achieving a set of guiding parameters, which are footprints of a correlated electronic topological state.
From the charge dynamics of LaAlGe and CeAlGe we indeed discover that the dispersion of the type II Weyl nodes (Fig 1.20) is affected by the strong band renormalisation due to the Kondo coupling mechanism at low temperatures in (4f1 orbitals) CeAlGe. This renormalisation greatly reduces the Fermi velocity (Fig 1.21) and remarkably enhances the charge carriers effective mass in CeAlGe with respect to LaAlGe, both effects being considered as fingerprint for the rare Weyl-Kondo state.
