Weyl-Kondo semimetals: extreme topological tunability and nonlinear optical signatures

Topological semimetals have been extensively studied in the weakly correlated regime. However, only recently models of gapless electronic topological phases with strong correlations - such as the Weyl-Kondo semimetal (WKSM) [1,2] – have been advanced, in convergence with the experiment on a corresponding topological heavy fermion semimetal Ce$_3$Bi$_4$Pd$_3$ [3]. In contrast to weakly correlated topology, completely different experimental signatures of nontrivial topology are needed for strongly correlated systems. These include the linear dispersion being probed through a $C=\Gamma T^3$ specific heat [1,3] and a giant nonlinear spontaneous Hall effect [3], both of which occur below the Kondo coherence temperature. In this talk, we will demonstrate how strong correlations lead to extreme topological tunability in the WKSM [4], illuminating the experiment in Ce$_3$Bi$_4$Pd$_3$ at high magnetic fields which observes topological transitions [5]. Remarkably, various Weyl nodal configurations form, dance through the Brillouin zone, and annihilate from the relatively-small Zeeman coupling to the f-electrons well-within the Kondo regime. Finally, we propose several nonlinear optical signatures to probe the highly singular Berry curvature from nodes pinned to the Fermi energy as predicted in WKSMs: high-harmonic generation, the circular photogalvanic effect, and the gyromagnetic effect. We present calculations of the high-harmonic generation spectrum of the WKSM model and discuss these results. Work at Rice has been supported by the NSF (DMR-1920740), the Robert A. Welch Foundation (C-1411) and the ARO (W911NF-14-1-0525). Work at Los Alamos was carried out under the auspices of the U.S. Department of Energy (DOE) National Nuclear Security Administration under Contract No.89233218CNA000001, and was supported by LANL LDRD Program. Work in Vienna was supported by the Austrian Science Fund (projects P29279 and P29296) and the European Community (H2020 project 824109).

[1] S. E. Grefe, H.-H. Lai, S. Paschen, Q. Si, PRB, 101, 075138 (2020); H.-H. Lai, S. E. Grefe, S. Paschen, Q. Si, PNAS, 115, 1 (2018).
[2] L. Chen et al. (S. E. Grefe), arXiv:2107.10837 (2021).
[3] S. Dzsaber et al. (S. E. Grefe), PNAS, 118, 8 (2021); ibid., PRL 118, 246601 (2017).
[4] S. E. Grefe, H.-H. Lai, S. Paschen, Q. Si, arXiv:2012.15841 (2020).
[5] S. Dzsaber et al., arXiv:1906.01182.