Gap states and valley-spin filtering in transition metal dichalcogenide monolayers

The magnetically induced valley-spin filtering in transition metal dichalcogenide monolayers $(M{X}₂$, where $M$ = Mo, W and $X$ = S, Se, Te) promises a new paradigm in information processing. However, the detailed understanding of this effect is still limited, regarding its underlying transport processes. Herein it is suggested that the filtering mechanism can be greatly elucidated by the concept of metal-induced gap states (MIGS), appearing in the electrode-terminated $M{X}₂$ materials, i.e., the referential filter setup. In particular, the gap states are predicted here to mediate valley- and spin-resolved charge transport near the ideal electrode/$M{X}₂$ interface, and therefore to initiate filtering. It is also argued that the role of MIGS increases when the channel length is diminished, as they begin to govern the overall valley-spin transport in the tunneling regime. In what follows, the presented study yields fundamental scaling trends for the valley-spin selectivity with respect to the intrinsic physics of the filter materials. As a result, it facilitates insight into the analyzed effects and provides design guidelines toward efficient valley-spin filter devices that are based on the discussed materials or other hexagonal monolayers with a broken inversion symmetry.