Method for encoding information by valley polarization in a material

Valleytronics is the technique of encoding, switching and storing information in the bandstructure of materials, namely in the valley degree of freedom. Upon proper excitation with an electromagnetic feld (e.g. a laser beam with an appropriate wavelength), one can induce an asymmetry of carriers between valleys in reciprocal space, in the following referred to as valley polarization, during resonant excitation of the bandgap in certain points in the bandstructure (such as the K or K’ points in a hexagonal lattice). The induction of valley polarization requires spatial inversion symmetry breaking and time inversion symmetry breaking that can be achieved using circularly polarized light for exciting carriers in monolayer materials such as transition-metaldichalcogenides.The present invention relates to a method for encoding information by valley polarization in a material using an electromagnetic field. The method comprises the steps of providing a material, and applying the electromagnetic field onto the material, wherein the electromagnetic field possesses an m-fold symmetry and the real-space lattice structure or real-space sub-lattice structure of the material possesses an n-fold symmetry, wherein the symmetry of the electromagnetic field corresponds to the symmetry of the real-space lattice structure or real-space sub-lattice structure of the material in such a way that n is an integer multiple of m, and wherein the electromagnetic field induces and/or manipulates valley polarization in the bandstructure of the material. The present invention further provides a device for generating an electromagnetic field suitable for inducing and/or manipulating valley polarization in a multilayer material.