Bias induced spin state transition mediated by electron excitations

Abstract

Recent experiments reported that spin-state transitions were realized by applying bias voltages. But these bias-induced spin state transitions (BISSTs) are not fully understood, especially the mechanism. It is well known that the metal-to-ligand charge transfer excitation (MLCT) and the metal-centered excitation (MC) activated by light radiation can induce the transition from low spin (LS) to high spin (HS) and that from HS to LS. Moreover, electronic excitations are accessible by inelastic cotunneling in molecular junctions with bias voltages applied. Based on these two experimental facts, we propose the MLCT basically leads to the BISST from LS to HS, and the MC results in the BISST from HS to LS. The rationality of the mechanism is demonstrated by comparing first-principles results and experimental observations. The calculated voltage threshold for activating the MLCT (MC) is close to the experimental voltage for observing the BISST from LS to HS (from HS to LS). The activation of MLCT (MC) depends on the bias polarity, which can explain the bias-polarity dependence of BISST in the experiment. Our study is important for further design of molecular spintronic devices working on spin state transition. a) huahao@pitt.edu b) zzeng@theory.issp.ac.cn 1 arXiv:1909.04254v1 [cond-mat.mes-hall]

Spin-Crossover in Supramolecular Iron(II)–2,6-bis(1H-Pyrazol-1-yl)pyridine Complexes: Toward Spin-State Switchable Single-Molecule Junctions

“…At the single-molecule level, intermolecular interactions cease to exist, and spin-state switching is achieved by applying a stimulus under isothermal conditions. − Charging of ligands, electric field-induced distortion of a molecule featuring a large dipole moment, and stretching a molecule in a single-molecule junction are some methods used to induce SCO at the single-molecule level. Electron-induced spin-state switching at the single-molecule level in surface-bound thin films of SCO active molecules has also been demonstrated in scanning tunneling microscope (STM) junctions at 2 K. − The spin-state switching at the single-molecule level is accompanied by conductance switching, and high-spin (HS) junctions show a spin-filtering effect, , elucidating the utility of spin-switchable molecular junctions as molecular spintronics elements.…”