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MoS2 thin-film transistors spin-states, of conduction electrons and vacancies, distinguished by operando electron spin resonance

Transition metal dichalcogenide MoS2 is a two-dimensional material, attracting much attention for next-generation applications thanks to rich functionalities stemmed from the crystal structure. Many experimental and theoretical works have focused on the spin-orbit interaction which couples the valley and spin degree of freedom so that the spin-states can be electrically controllable. However, the spin-states of charge carriers and vacancies have not been yet elucidated directly from a microscopic viewpoint. We report the spin-states in thin-film electric double-layer transistors using operando electron spin resonance (ESR) spectroscopy. We have observed clearly different ESR signals of the conduction electrons and vacancies, and distinguished the corresponding spin-states from the signals and theoretical calculations, evaluating the gate-voltage dependence and spin-susceptibility and g-factor temperature dependence. This analysis gives deep insight into the MoS2 magnetism and clearly indicates the lower charge mobilities compared to graphene, which would be useful for improvements of the device characteristics and new applications.