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Strongly correlated electron systems are known to exhibit a range of exotic phenomena, including strange metal behavior and unconventional superconductivity [1]. More recently, they are also discussed in the context of nontrivial band topology [2]. As the standard formulation of the latter relies on well-defined quasiparticles, one may ask whether topological characteristics can persist in regimes where the conventional band-structure description breaks down. Heavy fermion systems provide a natural setting to address this question, as quantum criticality of beyond order parameter type [1] and Weyl-Kondo semimetal behavior [3-5] have both been observed. Here, we study the non-centrosymmetric heavy fermion compound CeRu$_4$Sn$_6$, which is intrinsically quantum critical [6]. Our experiments reveal a topological semimetal phase emerging from the quantum critical regime, with a dome-like dependence on pressure and magnetic field. These results are understood by generalizing the concept of Weyl crossings to non-quasiparticle spectral functions overlapping at specific positions in momentum space [7]. This mechanism may also occur in other quantum critical systems of suitable symmetry, suggesting a new design principle for emergent topological phases.
[1] S. Paschen and Q. Si, Nat. Rev. Phys. 3, 9 (2021).
[2] J. G. Checkelsky et al., Nat. Rev. Mater. 9, 509 (2024)
[3] S. Dzsaber et al., Phys. Rev. Lett., 118, 246601 (2017)
[4] H.-H. Lai et al., Proc. Natl. Acad. Sci. U.S.A. 115, 93 (2018)
[5] S. Dzsaber et al., Proc. Natl. Acad. Sci. U.S.A. 118, e2013386118 (2021)
[6] W. T. Fuhrman et al., Sci. Adv. 7, eabf9134 (2021)
[7] D. M. Kirschbaum, L. Chen et al., Nat. Phys. 2, 218 (2026)
This work was supported by the Austrian Science Fund (FWF grants I4047, SFB F 86 “Q-M&S”, and I5868-N/FOR 5249 "QUAST"), the European Microkelvin Platform (H2020 project 824109), the European Research Council (ERC Advanced Grant 101055088-CorMeTop), and the US AFOSR (Grant FA8655-24-1-7018).