Current controlled spin states of van-der-Waals topological Fe₃GeTe₂

Electrical control of spin states is essential for both academic interest and the next-generation spin-related device applications. Very recently, 2D van-der-Waals (vdW) spin materials have rapidly flourished to become star members in the field of 2D materials and device physics. Among them, Fe₃GeTe₂ (FGT) received special attention because it is the only classic topological vdW spin metal. In this talk, I will show you our discovery of current-driven gigantic intrinsic spin-orbit torque in FGT, and then several cases of spin-based device application correspondingly. Finally, we experimentally demonstrate the symmetry anomaly, i.e., the inversion symmetry breaking in this previously-believed centrosymmetric system. Our surprising discovery and systematic investigation depict a prototypical route from fundamental physics to conceptual device applications, and also bring the exciting vdW spin materials to sharpen spin-related applications.

More detailed information is described below: we discover that an in-plane current can tune the hard spin state to a soft one in the nanoscale FGT devices, through a substantial reduction of coercive field. This surprising finding is possible because the in-plane current produces a highly unusual type of gigantic spin-orbit torque for single FGT itself without any heavy-metal layer. Such spin-orbit torque is directly related to the large Berry curvature and so its band topology. Furthermore, making use of this principle, we demonstrate a working model of new spin device, where highly efficient nonvolatile switching and multi-level states by the tiny current are achieved. Taking one more step forward, we develop this spin model to an all-vdW classic three-terminal SOT device of FGT/hBN/FGT heterostructure, whose spin configurations can be written by spin-orbit torque and read by tunneling spin-resistance separately. In addition, plateau-like spin-resistance is unexpectedly observed in twisted FGT/FGT homojunction without any spacer. On the other hand, inversion symmetry breaking is a general requirement for spin-orbit torque, which has been recently unveiled by our second harmonic generation in this previously-thought centrosymmetric material, finally settling the remaining puzzle.