Electrical generation and control of the valley carriers in a monolayer transition metal dichalcogenide

Abstract

Electrically controlling the flow of charge carriers is the foundation of modern electronics. By accessing the extra spin degree of freedom (DOF) in electronics, spintronics allows for information processes such as magnetoresistive random-access memory. Recently, atomic membranes of transition metal dichalcogenides (TMDCs) were found to support unequal and distinguishable carrier distribution in different crystal momentum valleys. This valley polarization of carriers enables a new DOF for information processing. A variety of valleytronic devices such as valley filters and valves have been proposed, and optical valley excitation has been observed. However, to realize its potential in electronics it is necessary to electrically control the valley DOF, which has so far remained a significant challenge. Here, we experimentally demonstrate the electrical generation and control of valley polarization. This is achieved through spin injection via a diluted ferromagnetic semiconductor and measured through the helicity of the electroluminescence due to the spin-valley locking in TMDC monolayers. We also report a new scheme of electronic devices that combine both the spin and valley DOFs. Such direct electrical generation and control of valley carriers opens up new dimensions in utilizing both the spin and valley DOFs for next-generation electronics and computing.

The 2017 Magnetism Roadmap

“…Semiconducting TMDs have a sizable band gap, and their crystal structure lacks an inversion centre, resulting in valence and conduction bands in nonequivalent valleys at the K and K′ points of the Brillouin zone. Because of the heavy atoms and outer d-orbitals, the SOC and associated spin splitting are large and the spin and valley degrees of freedom are strongly coupled, which can be used to control the valley polarization through spin injection or vice versa [16] (figure 4(a)). Optical excitation experiments have revealed long-lived and coherent spin dynamics in MoS 2 and WS 2 [17], and valley lifetimes of 40 ns in WSe 2 /MoSe 2 heterostructures [18].…”

Probing the Spin-Polarized Electronic Band Structure in Monolayer Transition Metal Dichalcogenides by Optical Spectroscopy

“…These properties have also been actively explored for new electronics and optoelectronics applications [4][5][6][7][8][9][10][11][12][13][14][15] . In the monolayer limit, group-VI TMDs (MX 2 , M = Mo, W; X = S, Se) are direct band-gap semiconductors with the fundamental energy gap located at the K and K' points of the Brillouin zone 16,17 .…”

Electrical spin injection and detection in molybdenum disulfide multilayer channel

“…Consequently, this yields a predicted short spin lifetime (10–200 ps)13 together with a small spin diffusion length (∼20 nm)14. Recently, a hole spin injection into ML TMDs has been demonstrated either with perpendicular magnetized GaMnAs injector15 or NiFe injector at large perpendicular magnetic field16 by electrical injection and optical detection method. This particularly emphasizes on the difficult issue to electrically inject and detect electron with in-plane spin polarization in a lateral ML MoS 2 device.…”