Bias induced spin state transition mediated by electron excitations

Area of Science:

• Molecular spintronics
• Quantum phenomena in molecular junctions

Background:

• Spin state transitions in molecular systems can be induced by external stimuli.
• Bias voltages in molecular junctions can induce electronic excitations.
• Light-induced spin transitions are known via metal-to-ligand charge transfer (MLCT) and metal-centered (MC) excitations.

Purpose of the Study:

• To elucidate the mechanism behind bias-induced spin state transitions in molecular junctions.
• To propose a model connecting electronic excitations to spin transitions under bias voltage.
• To provide a theoretical basis for designing molecular spintronic devices.

Main Methods:

• Theoretical modeling based on first-principles calculations.
• Comparison of theoretical predictions with experimental observations of spin transitions.
• Analysis of inelastic electron cotunneling in molecular junctions.

Main Results:

• Proposed that MLCT excitation drives low-spin (LS) to high-spin (HS) transitions under bias.
• Proposed that MC excitation drives HS to LS transitions under bias.
• Theoretical threshold voltages for MLCT and MC excitations align with experimental transition voltages.

Conclusions:

• The proposed mechanism successfully explains bias-induced spin state transitions and their polarity dependence.
• This work offers critical insights for the development of molecular spintronic devices.
• Understanding these mechanisms is key for controlling spin states via electrical bias.