Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals.

Mathias Gehlmann,Irene Aguilera,Ewa Młyńczak,Claus M Schneider,Markus Eschbach,Lukasz Plucinski,Beata Kardynał,Gustav Bihlmayer,Pika Gospodarič,Stefan Blügel,Stefan Cramm,Sven Döring

doi:10.1038/srep26197

Mathias Gehlmann, Irene Aguilera + Show 10 more

Open Access

https://doi.org/10.1038/srep26197

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Abstract

Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.

Highlights

The amplitude image of an atomic force microscope (AFM) in Fig. 1e shows the typical surface topography of a cleaved MoS2 single crystal and that the scotch tape method produces atomically flat areas at the MoS2 surface that largely exceed the maximum field of view of the AFM of 30 μm
Mahatha et al.[16] reported an inhomogeneous band bending in ARPES from areas with high step densities, which we observed in other areas of our samples
There is almost no change in the size of the splitting measured with different photon energies, which is a strong indication for a low out-of-plane dispersion and an in-plane confinement as we find it in the density functional theory (DFT) calculations

Summary

Introduction

Coupling (SOC) leads to a locking of the spin to layers. An indication for this spin-layer locking is the high circular polarization dependence of the photoluminescence for inversion-symmetric TMDC films, e.g. consisting of an even number of layers or bulk-like crystals[4,11,14]. With this report, our findings for bulk MoS2 and a recent publication[6] concerning the similar layered crystal WSe2 show that a spin-polarization can be observed, as long as the probing tool focuses on a specific layer in the bulk. We can show that these electronic states in the bulk material are almost completely confined within the plane of the layers and highly spin-polarized

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