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