Hyperfine interaction in atomically thin transition metal dichalcogenides

Abstract

Localization of charge carriers in monolayers (MLs) of transition metal dichalcogenides (TMDs) dramatically increases spin and valley coherence times, and, by analogy with other systems, the role of the hyperfine interaction should enhance. We perform theoretical analysis of the intervalley hyperfine interaction in TMD MLs based on the group representation theory. We demonstrate, that the spin-valley locking leads to the helical structure of the in-plane hyperfine interaction. In the upper valence band the hyperfine interaction is shown to be of the Ising type, which can be used for fabrication of the atomically thin quantum dots with the long spin and valley coherence times.

Dynamic Valley Polarization in Moire Quantum Dots

“…The spin and valley relaxation of excitons in TMDC monolayers can be related with the interplay between scattering of excitons and electron-hole exchange interaction or with the electron-phonon interaction [21][22][23][24]. However, for the individual non-interacting electrons and holes localized in MQDs in weak magnetic fields, these mechanisms are inefficient due to the absence of orbital motion and vanishing of electron-phonon interaction at zero frequency [25]. This is typical for the QDs made of the conventional semiconductors, where the spin relaxation in weak magnetic fields is driven by the hyperfine interaction [26].…”

“…For holes, B h N is directed along the z axis [25]. So it can not lead to the hole valley flips and does not play a role in exciton dynamics.…”

“…For electrons, by contrast, B e B can have all three components. This nuclear field is described by the Gaussian distribution function [25]…”

“…In Fig. 3 we use the dimensionless parameters, which can be associated with the following realistic values: 1/γ 0 = 10 ns [36,37], 1/γ = 10 µs [37], and /(|g e |µ B ∆ B ) = 100 ns [25]. The spatial separation of electron and hole suppresses the radiative recombination by ∼ 10 3 times, and we assume the same suppression for the exchange interaction.…”

“…Along with the electron valley polarization, the nuclear spins can also get polarized in the same conditions, if their relaxation time is long enough. In MoSe 2 the hyperfine interaction is the strongest with Se atoms [25] and if their spins get polarized, they effectively enhance the external magnetic field. Thus the shift of the maximum of the dynamic valley polarization to smaller fields with increase of the excitation power is possible.…”