Towards colloidal spintronics through Rashba spin-orbit interaction in lead sulphide nanosheets

Mohammad Mehdi Ramin Moayed,Thomas Bielewicz,Carmen Herrmann,Martin Sebastian Zöllner,Christian Klinke

doi:10.1038/ncomms15721

Mohammad Mehdi Ramin Moayed, Thomas Bielewicz + Show 3 more

Open Access

https://doi.org/10.1038/ncomms15721

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Abstract

Employing the spin degree of freedom of charge carriers offers the possibility to extend the functionality of conventional electronic devices, while colloidal chemistry can be used to synthesize inexpensive and tunable nanomaterials. Here, in order to benefit from both concepts, we investigate Rashba spin–orbit interaction in colloidal lead sulphide nanosheets by electrical measurements on the circular photo-galvanic effect. Lead sulphide nanosheets possess rock salt crystal structure, which is centrosymmetric. The symmetry can be broken by quantum confinement, asymmetric vertical interfaces and a gate electric field leading to Rashba-type band splitting in momentum space at the M points, which results in an unconventional selection mechanism for the excitation of the carriers. The effect, which is supported by simulations of the band structure using density functional theory, can be tuned by the gate electric field and by the thickness of the sheets. Spin-related electrical transport phenomena in colloidal materials open a promising pathway towards future inexpensive spintronic devices.

Highlights

Background currentJ0 0 mVÅ–1 J 0 J LPGE circular photo-galvanic effect (CPGE) 4/5 Σ Gate voltage (V) b 12CPGE current Normalized CPGE 5 mVÅ–1 0.12
Having introduced confinement and symmetry breaking by the gate electric field as the factors influencing the spin–orbit coupling (SOC), we separately studied these elements under the low illumination angle in order to tune the band splitting in the PbS nanosheets
The measurements indicate that by decreasing the thickness of the sheets, which corresponds to an increase of the confinement effect, structural inversion asymmetry and the Rashba SOC becomes more pronounced in PbS nanosheets

Summary

Introduction

By confining the material in z direction (height of the nanosheets), the symmetry is reduced first to the D4h point group and by application of asymmetric vertical interfaces on top and underneath (SiO2 and vacuum) as well as by the gate electric field, to C4v. All of these observations prove that the vertical asymmetry is able to generate a net CPGE current by changing the distribution of the carriers in the band structure, they do not exclude the possibility of local in-plane asymmetries, such as contacts or edges.

Results

Conclusion