Researchers from the CEMES and from the LPCNO have calculated the electronic and magnetic structure of the Co/MoS2 interface, using first principles methods based on the density functional theory. A perfect knowledge of the atomic structure and physical properties of this interface is necessary to perform high quality metallic contacts between a ferromagnetic electrode and a single MoS2 layer. It allows to design new spintronic devices, based on spin injection in the two-dimensional semiconductor MoS2.
- (a) : Structure atomique de la supercellule utilisée pour étudier l’interface Co/MoS2 (b) : Structure de bandes pour les électrons de spin majoritaire (les cercles rouges indiquent les bandes auxquelles contribue le feuillet de MoS2 ; la flèche bleue indique le bas de la bande de conduction de MoS2). (c) : Transferts de charge induits par la formation de liaisons covalentes aux interfaces Co/MoS2 (les lobes rouges et verts correspondent respectivement à un gain et à une perte d’électrons de spin majoritaire).
Single layer MoS
2 is a two-dimensional semiconductor with a direct optical bandgap the visible range. Inversion symmetry breaking and spin-orbit coupling result in a very peculiar band structure, with two families of non-equivalent valleys (
K and
K’). With such interesting characteristics, MoS
2 single layer is a perfect candidate for designing original spintronic devices, based on the manipulation of the spin and valley degrees of freedom which are intimately coupled in this material. This first requires to be able to inject a spin-polarized current in a single MoS
2 sheet. The possibility of this injection depends on the atomic, electronic and magnetic structures of the interface between a ferromagnetic electrode and MoS
2. In this context, we used first principles methods to calculated the atomic structure of the interface between a single MoS
2 layer (4x4-supercell) and the (0001) surface of hexagonal compact cobalt (5x5 supercell). The lowest energy interface atomic structure involves S atoms covalently bound to 1, 2 or 3 Co atoms. We calculated the band structure of this interface for majority and minority spin electrons. The conduction and valence bands of the isolated MoS
2 layer can be clearly identified on both sides of the Fermi level, together with new bands with energies inside the bandgap of MoS
2. These interface bands are the consequence of the chemical bonds between Co and S atoms at the interface ; they cross the Fermi level, giving to MoS
2 a metallic character, with a finite spin-polarization at the Fermi energy. We estimated that the height of the Schottky barrier between this metallic phase of MoS
2 and a free MoS
2 semiconducting channel far from the metallic contact is of 0.32 eV.
Reference
Electronic structure of the Co(0001)/MoS2 interface and its possible use for electrical spin injection in a single MoS2 layer
T. Garandel, R. Arras, X. Marie, P. Renucci, and L. Calmels
PHYSICAL REVIEW B 95, 075402 (2017)
https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.075402
Contact
Lionel Calmels – Professeur Université Paul Sabatier – CEMES-CNRS
