Abstract
The spin dynamics of localized charge carriers is mainly driven by hyperfine interaction with nuclear spins. Here we develop a theory of hyperfine interaction in transition metal dichalcogenide monolayers. Using group representation theory and the tight binding model we derive effective Hamiltonians of the intervalley hyperfine interaction in the conduction and valence bands. The spin–valley locking and pronounced spin–orbit splitting lead to a specific form of hyperfine interaction, which we call “helical”. We also demonstrate that the hyperfine interaction is noncollinear for chalcogen atoms in the general case. At the same time in the upper valence band the hyperfine interaction is purely of the Ising type, which suggests that the spin–valley polarization of localized holes in transition metal dichalcogenide monolayers can be conserved for a particularly long time.
Highlights
Thin transition metal dichalcogenides (TMDs), MX2 with M being a transition metal (Mo and W) and X being a chalcogen (S, Se, and T), represent a new generation of truly two-dimensional structures.[1]
The conduction and the valence bands at these points are split by the pronounced spin–orbit interaction, which leads to the so-called spin–valley locking and valley dependent optical selection rules.[4,5]
In practice TMD ML quantum dots can be made by chemical exfoliation[14,15,16] and lithographic nanopatterning[17] or charge carriers can be trapped by wrinkles,[18] homojunctions,[19] or defects.[20,21,22]
Summary
Thin transition metal dichalcogenides (TMDs), MX2 with M being a transition metal (Mo and W) and X being a chalcogen (S, Se, and T), represent a new generation of truly two-dimensional structures.[1]. We show that the low symmetry of TMD MLs allows for the noncollinear hyper ne interaction,[33,34] so the nuclear spins can be ipped without the need to ip the valley pseudospin This effect was previously observed in GaAs based quantum dots, where it manifested itself as a dragging of the quantum dot resonance frequency.[35] Our calculations show that this effect is about two orders of magnitude stronger in TMD ML quantum dots. In this work we demonstrate that it leads to a “helical” structure of the interaction of the valley pseudospin with nuclei, which means that the components of the hyper ne interaction Hamiltonian are periodically modulated in space This effect manifests itself in 2624 | Nanoscale Adv., 2019, 1, 2624–2632.
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