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O4.07 - Electrically Driven Valley Polarization by Spin Injection in a Monolayer Transition Metal Dichalcogenide Heterojunction 
April 8, 2015   11:45am - 12:00pm

Controlling the flow of electric charges enables nanoelectronics and modernizes the information technology. The spin degree of freedom of electrons embraces emerging spintronics, important to solid-state computing. The atomic membrane of transition metal dichalcogenides (TMDs) possesses a nonequivalent carrier distribution in crystal momentum space. The protection from its broken inversion symmetry makes the valley index of charge carriers a new degree of freedom for information processing. A variety of valleytronic devices such as valley filters, valves, and thermoelectric valley current have been proposed. Optical control and detection of valley polarization has been reported in monolayer TMDs due to the valley optical selection rules. However, electrical generation and control of valley-polarized carriers that is the key to the utilization of the valley degree of freedom in nanoelectronics, yet remains a formidable challenge. Here we experimentally demonstrate valley-polarized light emission by electrical spin-polarized carriers injection into monolayer WS2 using the ferromagnetic semiconductor, (Ga, Mn)As, as a spin aligner. The valley polarization is electrically generated due to the unique spin-valley locking, i.e., valley polarization is achieved through spin polarization of the charge carriers. Our valley polarization heterojunction becomes a circularly polarized light source due to the direct band gap and valley degree of freedom of monolayer WS2. The unique correlation between spin and valley indices of electric carriers opens the new dimension in utilizing both spin and valley for next-generation electronics and computing.

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