Magnetic Field-Insensitive and Temperature-Robust Spin-Valley Relaxation in h-BN Encapsulated Monolayer MoS₂

While conventional understanding holds that electron spin-valley relaxation in monolayer MoS₂ is highly sensitive to weak transverse magnetic fields and thermal activation, the research reveals a different scenario when monolayer MoS₂ is encapsulated in hexagonal boron nitride (h-BN). Using time-resolved Faraday rotation spectroscopy, it is found that the spin-valley dynamics in h-BN encapsulated monolayer MoS₂ are independent of transverse magnetic fields and only weakly dependent on temperature. Notably, the spin-valley polarization in h-BN encapsulated monolayer MoS₂ remains robust even at room temperature, exhibiting a biphasic behavior with lifetimes of 23 and 146 ps, attributed to itinerant electrons and trions, respectively. The study also clarifies the origin of the previously reported magnetic field-sensitive spin-valley component in monolayer MoS₂, demonstrating that it likely originates from localized states rather than itinerant electrons and is absent in h-BN encapsulated MoS₂. These findings not only update the understanding of spin-valley relaxation in monolayer MoS₂ but also provide insights into the complexity and diversity of spin-valley relaxation phenomena in monolayer transition metal dichalcogenides.