Weyl-Kondo semimetal: from heavy fermions to flat band systems

The interplay between topology and interactions has garnered great interest in the study of quantum matter. For metallic systems, the notion of Weyl Kondo semimetal has emerged as a rare example of gapless topological states driven by strong correlations [1,2]. Here we report two lines of recent work along this general direction. First, we introduce a general design principle, with the correlation-induced emergent excitations experiencing symmetry constraints and producing gapless topological states [3]. We also show that d-electron-based systems with geometry-induced flat bands can serve as new platforms for Weyl-Kondo semimetal [4,5]; this follows from a representation of the d-electron systems in terms of compact and extended molecular orbitals. Second, we show that flat-band systems can undergo a continuous selective transition [5] of the molecular orbitals and yields the associated quantum criticality. In this case, our findings connect with recent advances on heavy fermion quantum criticality [6], provide the first theoretical understanding of the observed strange metallicity in line-graph systems, and predict a phase diagram that has been supported by some very recent experiments on kagome metals [7].

[1] H.-H. Lai, S. E. Grefe, S. Paschen, and Q. Si, PNAS 115, 93 (2018); Phys. Rev. B 101, 075138 (2020)

[2] S. Dzsaber et al., PNAS 118, e2013386118 (2021); Phys. Rev. Lett. 118, 246601 (2017)

[3] L. Chen et al, Nat. Phys. 18, 1341 (2022); H. Hu et al., arXiv:2109.13224

[4] L. Chen et al, arXiv:2212.08017. H. Hu et al., Sci. Adv. 9, eadg0028 (2023)

[5] L. Chen et al, arXiv: 2307.09431

[6] H. Hu, A. Cai, L. Chen et al., arXiv:2109.13224; Q. Si et al, Nature 413, 804 (2001)

[7] Y. Liu et al., arXiv:2309.13514