and its field-tuned phase diagram*

The interplay of topology and strong electron correlations is emerging as a new frontier in quantum science; it is expected to bring forth exotic phases and excitations, as epitomized by the example of the fractional quantum Hall effect. Indeed, (weakly interacting) topological semimetals—featuring states with Dirac or Weyl dispersion in the bulk—were discovered when their correlation-driven counterparts were pursued. Heavy fermion systems provide an ideal setting because the Kondo interaction implements extreme correlation strength and representatives with strong spin-orbit coupling exist. A joint effort of experiments and theory has recently led to the discovery of a Weyl-Kondo semimetal phase [1-3]. Experimentally, it is realized in the noncentrosymmetric time reversal symmetry preserving heavy fermion semimetal Ce₃Bi₄Pd₃ [1,3]. This material has a Kondo temperature of 13 K [1] and remains paramagnetic down to at least 250 mK [3]. Our most striking observation is a giant spontaneous (zero-field) Hall effect, and an associated even-in-field Hall component, which provide direct evidence of Berry curvature singularities in close vicinity to the Fermi level [3]. These characteristics of Weyl physics develop only in the Kondo coherent state, and are thus manifestly correlation driven. The application of large magnetic fields leads to an annihilation of the Weyl nodes at a first critical field, and to the metallization of the system at a second one, featuring quantum criticality [4].

[1] S. Dzsaber et al., Phys. Rev. Lett. 118, 246601 (2017).
[2] H.-H. Lai et al., PNAS 115, 93 (2018).
[3] S. Dzsaber et al., arXiv:1811.02819
[4] S. Dzsaber et al., arXiv:1906.01182