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

Elucidating hole and electron states in organic semiconductor materials is one of the important issues for both their fundamental science and device applications. However, the detailed charge states, in particular, their spin states, have not yet been fully elucidated from a microscopic viewpoint. Here we show electrically controllable spin states of holes and electrons in typical organic semiconductor materials, a polymer regioregular poly­(3-hexyl­thiophene) (RR-P3HT) and a small molecule pentacene, using electron spin resonance (ESR) spectroscopy. By use of their ambipolar organic semiconductor devices, these states were revealed as a function of accumulated charge density. The spin states of the electrically accumulated electrons in RR-P3HT and pentacene are clarified for the first time. Moreover, the formation of spinless states of electrons in RR-P3HT and holes in pentacene are demonstrated under high charge density, showing a contrast to the spin states under low charge density. This result would be important for further understating hole and electron states in organic semiconductor materials and for improving the performance of organic semiconductor devices from a microscopic viewpoint.