Orbital gyrotropic magneto-electric effect and its strain engineering in monolayer NbX2
Abstract
Electrical control of the orbital degrees of freedom is an important area of research in the emerging field of "orbitronics." Orbital gyrotropic magneto-electric effect (OGME) is the generation of an orbital magnetization in a nonmagnetic metal by an applied electric field. Here, we show that strain induces a large GME in the monolayer NbX2 (X = S, Se) normal to the plane, primarily driven by the orbital moments of the Bloch bands as opposed to the conventional spin magnetization, without any need for spin-orbit coupling. The key physics is captured within an effective two-band valley-orbital model and it is shown to be driven by three key ingredients: the intrinsic valley orbital moment, broken C3z symmetry, and strain-induced Fermi surface changes. The effect can be furthermore switched by changing the strain condition, with potential for future device applications.