Nondegenerate valleys in the half-metallic ferromagnet ${\mathrm{Fe}/\mathrm{WS}}_{2}$

Nondegenerate valleys in the half-metallic ferromagnet ${Fe / WS}_{2}$

Omar Messaoudi, Julen Ibañez-Azpiroz, Hamid Bouzar, and Samir Lounis

Phys. Rev. B 97, 035404 – Published 3 January 2018

Abstract

We present a first-principles investigation of the electronic properties of monolayer ${WS}_{2}$ coated with an overlayer of Fe. Our ab initio calculations reveal that the system is a half-metallic ferromagnet with a gap of $\sim 1$ eV for the majority spin channel. Furthermore, the combined effect of time-reversal symmetry breaking due to the magnetic Fe overlayer and the large spin-orbit coupling induced by W gives rise to nondegenerate K and $K^{'}$ valleys. This has a tremendous impact on the excited-state properties induced by externally applied circularly polarized light. Our analysis demonstrates that the latter induces a singular hot-spot structure of the transition probability around the K and $K^{'}$ valleys for right and left circular polarization, respectively. We trace back the emergence of this remarkable effect to the strong momentum dependent spin-noncollinearity of the valence band involved. As a main consequence, a strong valley-selective magnetic circular dichroism is obtained, making this system a prime candidate for spintronics and photonics applications.

Received 11 October 2017
Revised 18 December 2017

DOI:https://doi.org/10.1103/PhysRevB.97.035404

Physics Subject Headings (PhySH)

Coatings Dichalcogenides Electronic structure Ferromagnets Half-metals Honeycomb lattice

Density functional theory Electromagnetic field calculations

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Omar Messaoudi^1,2, Julen Ibañez-Azpiroz¹, Hamid Bouzar², and Samir Lounis¹

¹Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich & JARA, D-52425 Jülich, Germany
²Laboratoire de Physique et Chimie Quantique (LPCQ), Université Mouloud Mammeri Tizi-Ouzou, BP 17 RP, 15000 Tizi-Ouzou, Algérie

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Vol. 97, Iss. 3 — 15 January 2018

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Figure 1
Crystal structure of ${Fe / WS}_{2}$ . Panels (a) and (b), respectively, show the side and top views. (c) Primitive two-dimensional Brillouin zone with high symmetry labels.
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Figure 2
Calculated electronic structure for ${Fe / WS}_{2}$ . (a) Calculated Band structure both in the scalar relativistic and fully relativistic cases. The red and blue lines represent, respectively, the spin-up and spin-down of the scalar relativistic calculation, while the dashed black line represents the fully relativistic bands. (b) Calculated scalar density of states, where as for the band structure the red and blue lines represent, respectively, the spin-up and spin-down contributions. (c) Calculated projected density of states for the main contributions near the Fermi level. The black line represents the electron $d$ states of Fe and the dashed orange line represents the electron $d$ states of W. The rest of channels have a negligible contribution in this energy range.
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Figure 3
Momentum-dependent spin-polarization for the conduction and valence bands. (a) Fully relativistic band structure highlighting the two bands of interest. The thick solid line represents the conduction band labeled $A$ while the thick dashed line represent the valence band labeled $B$ . The rest of the bands are represented with thin dashed lines with high transparency. (b) Momentum-dependent spin polarization plotted in the full Brillouin zone. The background color represents the spin polarization along the $z$ direction while the white arrows represent the in-plane components. The solid and dashed lines represent the calculated Fermi surfaces for $A$ and $B$ , respectively.
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Figure 4
(a) Schematic representation of left circularly polarized (LCP) and right circularly polarized (RCP) light excitation of ${Fe / WS}_{2}$ , $\bar{A}$ represents the vector potential associated with the field. LCP and RCP carry spin angular momentum $+ ℏ$ and $- ℏ$ , respectively. (b) Calculated absorption rate associated with the spin-flip transitions, the blue dashed and red solid lines correspond to the absorption of left circularly polarized (LCP) and right circularly polarized (RCP) light, respectively. Panels (c) and (d) represent the Spin-flip transition probabilities associated with the conduction band ( $A$ ) and the valence band ( $B$ ) for left circularly polarized (LCP) and right circularly polarized (RCP) light, respectively. The Fermi surface for each band is indicated by solid line for $A$ and a dashed line for $B$ .
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Physical Review B

covering condensed matter and materials physics

Nondegenerate valleys in the half-metallic ferromagnet ${Fe / WS}_{2}$

Omar Messaoudi, Julen Ibañez-Azpiroz, Hamid Bouzar, and Samir Lounis

Phys. Rev. B 97, 035404 – Published 3 January 2018

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Physical Review B

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Nondegenerate valleys in the half-metallic ferromagnet Fe/WS2

Omar Messaoudi, Julen Ibañez-Azpiroz, Hamid Bouzar, and Samir Lounis

Phys. Rev. B 97, 035404 – Published 3 January 2018

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Nondegenerate valleys in the half-metallic ferromagnet ${Fe / WS}_{2}$