First-principle modelling of supramolecular spin valves: from the operational principle to the effective control

• Applicant: Professor Dr. Wolfgang Wenzel, since 5/2022
• Subject Area: Theoretical Condensed Matter Physics
• Term: from 2018 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 404084478

Over the last two decades, molecular electronics has advanced rapidly in terms of both experimental techniques and theory. Modern experimental techniques allow fabrication and characterization of molecular junctions. Recent investigations have also focused on manipulation of the spin, as an intrinsic degree of freedom of an electron, in addition to the ‘external’ (spatial) degrees of freedom. Going beyond charge transport, this proposal is focused on a specific realization of molecular spintronics, where single molecular magnets (SMMs) integrated into the nanojunction provide localized magnetic moments and interact with the current. Presently there is no quantitative model to describe these effects. In this project we are going to establish theoretical foundations to explain the mechanism and improve the performance of supramolecular spintronic devices, which are based on a carbon nanotube (CNT) decorated with several single molecular magnets. A giant magnetic resistance of 300% was experimentally observed in first realizations of CNT decorated with a single SMM, which means they operate as a spin-valve. Unlike known spin-valve devices, which require ferromagnetic electrodes, the role of spin polarizer and spin analyser in the supramolecular spin-valves investigated here is played by single-molecular magnets, and the rest of the valve consist of nonmagnetic materials (CNT and non-magnetic metal electrodes). This setup makes SMM-CNT spin valves a suitable candidate for various practical applications, i.e. quantum computers. In this project we will use combined first-principles calculations of the electronic structure (e.g. density functional theory (DFT) or beyond) combined with the nonequilibrium Green function formalism (NEGF) to elucidate, how electron current through the nanotube is affected by the relative orientation of the single-molecular magnets. This requires an effective and specialized combination of the DFT and NEGF and the establishment of advanced computational methods, which will be integrated into existing program packages. In collaboration with the experimental group of Prof. Wernsdörfer at KIT we will possible ways to control SMMs dipole orientation, e.g. the local gates, to (1) the effect of the SMMs spins noncollinearity and (2) the advantage of using nanocarbon materials other than carbon nanotube as the spin-valve channel.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Artem Fediai, until 5/2022