Emergent topological state in a quantum critical heavy fermion system

Heavy fermion systems exhibit various fascinating phenomena, from strange metal behavior and unconventional superconductivity to correlation-driven topology [1]. Such features are also discussed in the context of other strongly correlated material platforms, with Kondo physics serving as a unifying theme [2]. The Weyl-Kondo semimetal state [3-5] realized in Ce₃Bi₄Pd₃ [3,5] is a prime example of a gapless topological phase driven by the Kondo effect. Using the heavy fermion compound CeRu₄Sn₆, which exhibits a quantum critical point of beyond order parameter type [6], we address the question of whether topological phases can form even in the absence of Landau quasiparticles. Our experiments reveal a topological semimetal phase that emerges from the system’s quantum critical state and exhibits a dome-like shape as a function of pressure and magnetic field. These findings are understood by generalizing the concept of Weyl crossings to non-quasiparticle spectral functions overlapping in energy at specific positions in momentum space [7]. We anticipate that this situation may also occur in other quantum critical systems of suitable symmetry, thus pointing to a new design principle for emergent topological phases.

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[2] J. G. Checkelsky et al., Nat. Rev. Mater. 9, 509 (2024)

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[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., arXiv:2404.15924 (2024), to appear in Nat. Phys.