Broken Edge Spin-Symmetry Induces Spin-polarized Current in Graphene Nanoribbon

28 August 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Zig-zag graphene nanoribbons (ZGNRs) are known to possess spin moments at the hydrogen- terminated edge carbon atoms, thus the spin-polarized electron transmission is expected while the current is longitudinally passed through the ZGNRs. However, in pristine ZGNRs, the spin polarized transmission is not observed due to symmetric anti-parallel distributions of the spin densities between the edges. Here, the hypothesis is, any physical or chemical process that breaks such anti-parallel spin-symmetry can induce spin-polarized transmission in the ZGNRs. In this work, we have established this proof-of-concept by depositing the trimethylenemethane (TMM) radical on 6ZGNRH and investigating the quantum transport properties by employing the density functional theory in conjunction with nonequilibrium Green’s function (DFT-NEGF) method. Although TMM has a high magnetic moment (2 µB ), it does not induce magnetization in 6ZGNRH when TMM is physisorbed. But, during the chemisorption of TMM, it forms the π − π bond with the 6ZGNRH in a particular geometric configuration where the pz orbitals of carbon atoms of TMM have maximum overlap with the pz orbitals of carbon atoms of 6ZGNRH. The chemisorption of TMM transfers the spin moment to 6ZGNRH, which breaks the edge spin-symmetry of pristine 6ZGNRH. The adsorption of TMM radical results in transmission dips in the transmission spectra due to interference between localized states of TMM and 6ZGNRH states. This induces spin-polarized transmission with 60% spin-filtering efficiency (SFE) at zero bias, which can further be enhanced up to 92% by applying the bias voltage of 1.0 V.

Keywords

Graphene Nanoribbons
Spin Filtering Efficiency
Quantum Interference
NEGF-DFT
Electron Transport

Supplementary materials

Title
Description
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Title
Supporting Information - Broken Edge Spin-Symmetry Induces Spin-polarized Current in Graphene Nanoribbon
Description
Geometric and electronic structure analysis of TMM adsorbed 4ZGNRH and 12ZGNRH, Electron transmission in pristine 4ZGNRH and 12ZGNRH, Effect of TMM adsorption on transport properties of 4ZGNRH and 12ZGNRH. Effects of bias voltage on SFE.
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