Valley-symmetry-broken magnetic topological responses in (Pt/Pd)₂HgSe₃/CrGeTe₃ and Pd₂HgSe₃/CrI₃ through interfacial coupling

Bringing together spin, valley, topology, and layer degrees of freedom on a single platform could establish an efficient way to engineer phenomena such as valley-symmetry-broken magnetic topological insulators. Here, we combine van der Waals (vdW) layered ferromagnetic insulators (CrGeTe3 and CrI3) and Kane-Mele-type topological insulators (Pt2HgSe3 and Pd2HgSe3) in the form of heterobilayers. We find that the mutual interfacial coupling turns the helical nature in (Pt/Pd)(2)HgSe3 layers to the chiral topological nature with a large valley polarization. In particular, we identify (Pt/Pd)(2)HgSe3/CrGeTe3 and Pd2HgSe3/CrI3 as quantum anomalous Hall insulators supporting a large valley polarization platform together with sizable nontrivial global band gaps similar to 32, 17, and 16 meV at the Fermi surface, respectively. Meanwhile, the appearance of considerable orbital magnetization in (Pt/Pd)(2)HgSe3 layers can cause a measurable optical Kerr effect in this family of materials. Furthermore, we observe the layer-type band inversion around a single valley driven by the spin-orbit coupling in the (Pt/Pd)(2)HgSe3/CrGeTe3 heterobilayers, which are very rarely found in vdW layered solids. Moreover, the (Pt/Pd)(2)HgSe3 enhances the ferromagnetic properties, such as Curie temperature of CrGeTe3 in comparison to its freestanding form. Interestingly, the interfacial coupling of (Pt/Pd)(2)HgSe3 drives the in-plane magnetic anisotropy energy of the freestanding CrGeTe3 to the out-of-plane direction. In contrast, the Pt2HgSe3 layer switches the out-of-plane magnetic anisotropy energy of freestanding CrI3 to the in-plane direction of the sample via an interfacial hybridization. We attribute this switching of magnetic anisotropy energy in (Pt/Pd)(2)HgSe3/CrGeTe3 and Pt2HgSe3/CrI3 heterobilayers to the dominant contribution of the spin-conserving processes (vertical bar Delta S-z vertical bar = 0 and vertical bar Delta m(z)vertical bar = 0) and (vertical bar Delta S-z vertical bar = 0 and vertical bar Delta m(z)vertical bar = 1) in overall magnetic anisotropy energy, respectively. Our study may foster a suitable platform in which various degrees of freedom can be gathered to realize topological spintronics and valleytronics-based applications.