Topological Kondo semimetal and insulator in AB-stacked heterobilayer transition metal dichalcogenides

Abstract

Recent experiments reported the realization of a heavy Fermi liquid in AB-stacked MoTe$_2$/WSe$_2$ heterobilayers. In this paper we show that the AB-stacked heterobilayer configuration is particularly suited to realize topological Kondo semimetal and topological Kondo insulator ground states at a doping of two holes per moir\'e unit cell. The small lattice mismatch between the MoTe$_2$ and WSe$_2$ monolayers and the different bandwidths of their highest lying moir\'e valence bands means that, in the experimentally relevant range of hole dopings, the MoTe$_2$ layer is effectively a Mott insulator with only low-lying magnetic excitations Kondo-coupled to more itinerant electrons in the WSe$_2$. The crucial consequence of the AB-stacking configuration is that the interlayer tunnelling connects orbitals of opposite parity in the two layers, leading to a chiral Kondo coupling. We show that the chiral Kondo coupling favors a topological Kondo semimetal at filling $\nu=1+1$, with a non-quantized spin Hall conductance arising from edge modes, whose spectrum and overlap with bulk states we determine. We further show that a spatially random strain field that locally breaks the rotation symmetry can convert the Kondo semimetal to a narrow gap topological Kondo insulator featuring a quantized spin Hall conductance.