Quantum spin sensors for open-shell molecules

Abstract

Zigzag graphene nanoribbons (ZGNRs) exhibit symmetric, but opposite spin distributions on their edges, making them susceptible to perturbations due to molecular adsorption. This study investigates the impact of the adsorption of closed-shell (e.g. N₂, CO, CO₂) and open-shell paramagnetic (e.g. O₂, NO, NO₂) molecules on the spin-polarized quantum transport properties of zigzag graphene nanoribbons using density functional theory and nonequilibrium Green's function (NEGF-DFT) methods. We found that closed-shell molecules physisorbed on graphene nanoribbons, while open-shell molecules chemisorbed strongly at the edges. This chemisorption disrupts the symmetric spin distribution, leading to spin-polarized transmission. The underlying mechanism for spin-polarized transmission in open-shell molecule adsorption cases is the quantum interference between the localized and delocalized hybridized states of molecule adsorbed graphene nanoribbons. The analysis of bond current, the current between a pair of two atoms, shows that physisorbed closed-shell molecules act as a scattering center, which reduces the current through graphene nanoribbons. We showed that the interaction of open-shell molecules with the graphene nanoribbons depends on the electronic properties of adsorbed molecules. Thus, a variation in the destructive quantum interference pattern is observed for different open-shell molecules resulting in different spin currents. This phenomenon can be used for molecular recognition of open-shell paramagnetic species, providing avenues for quantum spin sensor technology.