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

Abstract

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 (${\mathrm{CrGeTe}}_{3}$ and ${\mathrm{CrI}}_{3}$) and Kane-Mele-type topological insulators (${\mathrm{Pt}}_{2}{\mathrm{HgSe}}_{3}$ and ${\mathrm{Pd}}_{2}{\mathrm{HgSe}}_{3}$) in the form of heterobilayers. We find that the mutual interfacial coupling turns the helical nature in ${(\mathrm{Pt}/\mathrm{Pd})}_{2}{\mathrm{HgSe}}_{3}$ layers to the chiral topological nature with a large valley polarization. In particular, we identify ${(\mathrm{Pt}/\mathrm{Pd})}_{2}{\mathrm{HgSe}}_{3}/{\mathrm{CrGeTe}}_{3}$ and ${\mathrm{Pd}}_{2}{\mathrm{HgSe}}_{3}/{\mathrm{CrI}}_{3}$ as quantum anomalous Hall insulators supporting a large valley polarization platform together with sizable nontrivial global band gaps $\ensuremath{\sim}$ 32, 17, and 16 meV at the Fermi surface, respectively. Meanwhile, the appearance of considerable orbital magnetization in ${(\mathrm{Pt}/\mathrm{Pd})}_{2}{\mathrm{HgSe}}_{3}$ 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 ${(\mathrm{Pt}/\mathrm{Pd})}_{2}{\mathrm{HgSe}}_{3}/{\mathrm{CrGeTe}}_{3}$ heterobilayers, which are very rarely found in vdW layered solids. Moreover, the ${(\mathrm{Pt}/\mathrm{Pd})}_{2}{\mathrm{HgSe}}_{3}$ enhances the ferromagnetic properties, such as Curie temperature of ${\mathrm{CrGeTe}}_{3}$ in comparison to its freestanding form. Interestingly, the interfacial coupling of ${(\mathrm{Pt}/\mathrm{Pd})}_{2}{\mathrm{HgSe}}_{3}$ drives the in-plane magnetic anisotropy energy of the freestanding ${\mathrm{CrGeTe}}_{3}$ to the out-of-plane direction. In contrast, the ${\mathrm{Pt}}_{2}{\mathrm{HgSe}}_{3}$ layer switches the out-of-plane magnetic anisotropy energy of freestanding ${\mathrm{CrI}}_{3}$ to the in-plane direction of the sample via an interfacial hybridization. We attribute this switching of magnetic anisotropy energy in ${(\mathrm{Pt}/\mathrm{Pd})}_{2}{\mathrm{HgSe}}_{3}/{\mathrm{CrGeTe}}_{3}$ and ${\mathrm{Pt}}_{2}{\mathrm{HgSe}}_{3}/{\mathrm{CrI}}_{3}$ heterobilayers to the dominant contribution of the spin-conserving processes ($|\mathrm{\ensuremath{\Delta}}{S}_{z}|=0$ and $|\mathrm{\ensuremath{\Delta}}{m}_{z}|=0$) and ($|\mathrm{\ensuremath{\Delta}}{S}_{z}|=0$ and $|\mathrm{\ensuremath{\Delta}}{m}_{z}|=1$) 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.