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In heavy fermion systems the Kondo effect stabilizes strongly renormalized heavy electronic bands, and promotes novel quantum phases and excitations. Recently, the discovery of topologically non-trivial insulators, as well as Dirac and Weyl semimetals with 3D bulk linear electronic dispersion has triggered a lot of interest. So far, investigations have focused on non-interacting settings, but it is of great interest to also explore the interplay of strong correlations and topology. For this purpose we have searched for topologically non-trivial phases in heavy fermion systems. Indeed, by tuning the spin-orbit coupling strength by Pt-Pd substitution in Ce₃Bi₄(Pt,Pd)₃, we have discovered a transformation from a Kondo insulator in Ce₃Bi₄Pt₃ to a semimetal in Ce₃Bi₄Pd₃ [1]. The latter shows the thermodynamic hallmark of strongly renormalized linear electronic bands [1], as recently predicted for a Weyl-Kondo semimetal [2]. Strikingly, as full Kondo coherence sets in, a large spontaneous Hall effect appears. As the material is entirely nonmagnetic, this is direct evidence of a huge Berry curvature dipole in the absence of time-reversal symmetry breaking. We attribute this effect to the topological nature of this noncentrosymmetric material, in the form of tilted Kondo-driven Weyl nodes [3].


[1] S. Dzsaber, L. Prochaska, A. Sidorenko, G. Eguchi, R. Svagera, M. Waas, A. Prokofiev, Q. Si, and S. Paschen, Kondo insulator to semimetal transformation tuned by spin-orbit coupling, Phys. Rev. Lett. 118, 246601 (2017).
[2] H.-H. Lai, S. E. Grefe, S. Paschen, and Q. Si, Weyl–Kondo semimetal in heavy-fermion systems, Proc. Natl. Acad. Sci. USA 115, 93 (2018).
[3] S. Dzsaber, X. Yan, G. Eguchi, A. Prokofiev, T. Shiroka, P. Blaha, O. Rubel, S. E. Grefe, H.-H. Lai, Q. Si, and S. Paschen, Giant spontaneous Hall effect in a nonmagnetic Weyl-Kondo semimetal, arXiv:1811.02819 (2018).