다층 WSe2 및 MoSe2의 초고속 유사 스핀 양자 비트

 0 with an exponentially-damped cosine function \(S(\nu,{\tau }_{v})\propto \exp (-{{\Delta }}t/{\tau }_{v})\cos (2\pi \nu \Delta t)\) for delay times Δt well above the fast initial decay of the TRFE signals, as exemplarily shown by the red solid line in Fig. 2c for the 9 T trace. An important result is that the oscillations with frequency ν at B∥ > 0 decay with approximately the same decay time τv as the excitonic signal at B∥ = 0, and no long-lived oscillatory signal is developed. From that we conclude that the oscillations stem from a Larmor precession of the exciton magnetic moment, and not from the spin of background charge carriers, as observed for localized electrons in MoS2 and WS2 monolayers44. Furthermore, the approximate independence of the decay time τv from B∥ shows that g factor fluctuations do not play a role. Otherwise, a 1/B∥ dependence of τv would be expected45,46. Figure 3a shows a summary of all oscillation frequencies ν, extracted by this procedure, versus B∥. Clearly, a linear, Zeeman-like dependence can be recognized. The determined ∣g∥∣ are given in the legend of Fig. 3a. The experimental error margins for these values are about ±0.2. It should be noted that with TRFE experiments we can only determine the magnitude of the g factor but not its sign. Very remarkably, for all excitonic resonances, the determined ∣g∥∣ are very close to out-of-plane g factors, ∣g⊥∣, of the corresponding materials, reorted in refs. 25, 28, which are for WSe2 bulk material ∣g⊥∣ = 3.2 ± 0.2 and 3.3 ± 0.6 for the A1s and A2s intralayer excitons, respectively25. For MoSe2 bulk, the reported value for A1s is ∣g⊥∣ = 2.7 ± 0.125. Hence, we conclude that ∣g∥∣ ~ ∣g⊥∣ for multilayer TMDCs, approaching the bulk limit./p> 0 in a multilayer. For the excitons, the z component of the spin of the electron is symbolized by a small arrow with a single line, while the hole spin is indicated by an arrow with a double line. Energy splittings of the excitons due to finite g∥ are taken into account. The red double arrows should symbolize the coherent momentum-allowed oscillation between adjacent layers. c Representation of the pseudospin rotation on a Bloch sphere. The north pole corresponds to τ = +1, while the south pole represents the τ = −1 state. The orange arrow would correspond to a system, excited with linearly-polarized light./p>