Electrical valley excitation by spin injection in monolayer TMDC

The spin degree of freedom (DOF) of electrons was exploited for information processes such as magnetoresistive random-access memory and gave birth to the field of spintronics. Recently, the valley index, a new DOF, was discovered originated from an unbalanced carrier distribution in the momentum space in atomic membrane transition metal dichalcogenides (TMDCs), and optical valley excitation has been observed. However, electrical control of valley freedom remains the major challenge for realizing its potential in electronics. Here, we demonstrate electrically driven valley polarization and report a new scheme of electronic devices combining both spin and valley DOFs. Valley polarization is electrically generated through spin injection and measured by the helicity of electroluminescence. The electrical generation and the control of valley polarization in 2D semiconductors open a new dimension for spin-valley based electronics.