Negative Differential Resistance in Spin-Crossover Molecular Devices

Abstract

We demonstrate, based on low-temperature scanning tunneling microscopy (STM) and spectroscopy, a pronounced negative differential resistance (NDR) in spin-crossover (SCO) molecular devices, where a FeII SCO molecule is deposited on surfaces. The STM measurements reveal that the NDR is robust with respect to substrate materials, temperature, and the number of SCO layers. This indicates that the NDR is intrinsically related to the electronic structure of the SCO molecule. Experimental results are supported by density functional theory (DFT) with nonequilibrium Green’s function (NEGF) calculations and a generic theoretical model. While the DFT+NEGF calculations reproduce NDR for a special atomically sharp STM tip, the effect is attributed to the energy-dependent tip density of states rather than the molecule itself. We, therefore, propose a Coulomb blockade model involving three molecular orbitals with very different spatial localization as suggested by the molecular electronic structure.

Computational demonstration of isomer- and spin-state-dependent charge transport in molecular junctions composed of charge-neutral iron(ii) spin-crossover complexes

“…Several of the features present in the I versus V profiles of the complexes-for example, the strong spin-down polarization of the current, highly bias-dependent transmission spectra, and NDR effects, have been reported in previous theoretical studies detailing the spin-polarized transport properties of iron(II) SCO complexes utilizing Au(111) nanowires as electrodes. 32,71 Regarding the mechanisms underlying the NDR, a recent DFT-NEGF-based study suggests 72 that the local electronic structure of the electrodes could lead to the appearance of artificial NDR effects. Without discarding an artefact of the model itself, the observed NDR effect may be associated with a physical effect related to the displacement of molecular states close to the Fermi level under the effect of bias.…”

High-Sensitivity Microthermometry Method Based on Vacuum-Deposited Thin Films Exhibiting Gradual Spin Crossover above Room Temperature

“…Yet, it remains crucial to develop further high-quality thin films and other micro−nano objects of SCO materials displaying robust, near-roomtemperature SCO combined with the desired (optical, electrical, and mechanical) functionalities. 38…”

“…This work extends the limited portfolio of SCO compounds for demanding microthermometry applications and highlights once again the technological interest of this family of stimuli-responsive molecular materials. Yet, it remains crucial to develop further high-quality thin films and other micro–nano objects of SCO materials displaying robust, near-room-temperature SCO combined with the desired (optical, electrical, and mechanical) functionalities. − …”

An iron(II) complex shows bistable spin-state switching characteristic with T1/2 centred at room temperature

“…Finally, the grand old phenomenon of SCO continues to evolve keeping abreast with the contemporary developments in molecular magnetism and related topics. 5,[28][29][30][31][32][33][34][35][36][37][38][39] We are happy that the topic has chosen us to express interesting facets, as discussed in this script.…”