Electrically Pumped Valley Emitter in Transition Metal Dichalcogenides with Magnetic Manipulation.

Optical pumping has been extensively employed as a straightforward and efficient method for the investigation of excitonic effects in 2D transition metal dichalcogenides (TMDCs). However, the challenge of achieving well-matched resonant excitation makes it difficult to conduct a comprehensive and rigorous comparative study across different TMDCs systems. In this work, electrical pumping is utilized on quantum well structures of TMDCs, enabling equivalent carrier injection with similar kinetic energy while effectively mitigating the effects of non-resonant excitation. Valley-polarized electroluminescence (VP-EL) is systematically investigated under varying magnetic fields, demonstrating that without magnetic electrodes or substrates, reversing the magnetic field direction induces a corresponding reversal in the EL valley polarization. A comparative analysis of VP-EL from monolayer WS, its homobilayer (WS/WS), and heterobilayer (WS/WSe) reveals that large spin-orbit coupling (SOC) and dark exciton ground state of WS enable the polarization reversal tunable by interlayer charge transfer and spin-matched interlayer hopping. This work elucidates the roles of SOC and the excitonic states for magneto-electroluminescence and demonstrates electrical pumping as a vital technique for the exploration of optical properties of 2D semiconductors.