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Physical properties of the Co(0001)/MoS2 interface for spin injection in a single MoS2 layer

Published in Physical Review B. (2017)

by PREVOTS Evelyne, PREVOTS Evelyne - published on , updated on

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.

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(a) : Atomic structure of the supercell used to study the Co/MoS2 interface (b) : Majority spin electron band structure (red circles indicate the contribution of the MoS2 layer) ; the bleue arrow shows the bottom of the MoS2 conduction band. (c) : Majority spin charge transfers induced by chemical bonding at the Co/MoS2 interface (red and green colors respectively correspond areas with an increase and a decrease of the electron density).

Single layer MoS2 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, MoS2 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 MoS2 sheet. The possibility of this injection depends on the atomic, electronic and magnetic structures of the interface between a ferromagnetic electrode and MoS2. In this context, we used first principles methods to calculated the atomic structure of the interface between a single MoS2 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 MoS2 layer can be clearly identified on both sides of the Fermi level, together with new bands with energies inside the bandgap of MoS2. 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 MoS2 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 MoS2 and a free MoS2 semiconducting channel far from the metallic contact is of 0.32 eV.



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)



Lionel Calmels – Professeur Université Paul Sabatier – CEMES-CNRS