Valley polarization in MoS₂ monolayers by optical pumping Researchers have demonstrated that circularly polarized light can selectively excite degenerate valleys in MoS₂ monolayers, leading to valley polarization. This discovery is significant for valleytronics, a new field of electronics that uses valley index instead of spin for information processing. The study shows that over 30% valley polarization can be achieved in pristine MoS₂ monolayers, indicating the potential for optical valley control. MoS₂ is a two-dimensional semiconductor with unique optical and transport properties. Its electronic structure allows for valley-dependent optical selection rules, which are crucial for valleytronics. The inversion symmetry breaking in monolayers leads to valley-contrasting optical selection rules, enabling valley-dependent interactions with light. This is in contrast to bilayers, where inversion symmetry is preserved, and valley-dependent selection rules are not allowed. The study used polarization-resolved luminescence to observe valley polarization. The results showed that the circular polarization of the emitted light matched the polarization of the excitation light, indicating valley polarization. The polarization was not affected by an in-plane magnetic field, ruling out spin polarization as the cause. This is because valley polarization is not affected by magnetic fields, unlike spin polarization. The study also compared the luminescence of monolayers and bilayers. Monolayers showed significant circular polarization, while bilayers did not, consistent with the inversion symmetry breaking in monolayers. The circular polarization was observed to decrease with temperature, indicating that valley scattering becomes more significant at higher temperatures. The results demonstrate that MoS₂ monolayers can be used for valleytronics and spintronics applications. The study provides a viable method for generating and detecting valley polarization in MoS₂ monolayers, which could lead to new electronic devices. The findings are supported by experimental data and theoretical models, showing the potential of MoS₂ in future electronics.Valley polarization in MoS₂ monolayers by optical pumping Researchers have demonstrated that circularly polarized light can selectively excite degenerate valleys in MoS₂ monolayers, leading to valley polarization. This discovery is significant for valleytronics, a new field of electronics that uses valley index instead of spin for information processing. The study shows that over 30% valley polarization can be achieved in pristine MoS₂ monolayers, indicating the potential for optical valley control. MoS₂ is a two-dimensional semiconductor with unique optical and transport properties. Its electronic structure allows for valley-dependent optical selection rules, which are crucial for valleytronics. The inversion symmetry breaking in monolayers leads to valley-contrasting optical selection rules, enabling valley-dependent interactions with light. This is in contrast to bilayers, where inversion symmetry is preserved, and valley-dependent selection rules are not allowed. The study used polarization-resolved luminescence to observe valley polarization. The results showed that the circular polarization of the emitted light matched the polarization of the excitation light, indicating valley polarization. The polarization was not affected by an in-plane magnetic field, ruling out spin polarization as the cause. This is because valley polarization is not affected by magnetic fields, unlike spin polarization. The study also compared the luminescence of monolayers and bilayers. Monolayers showed significant circular polarization, while bilayers did not, consistent with the inversion symmetry breaking in monolayers. The circular polarization was observed to decrease with temperature, indicating that valley scattering becomes more significant at higher temperatures. The results demonstrate that MoS₂ monolayers can be used for valleytronics and spintronics applications. The study provides a viable method for generating and detecting valley polarization in MoS₂ monolayers, which could lead to new electronic devices. The findings are supported by experimental data and theoretical models, showing the potential of MoS₂ in future electronics.