Engineering Valley Polarization of Monolayer WS₂: A Physical Doping Approach

Abstract

The emerging field of valleytronics has boosted intensive interests in investigating and controlling valley polarized light emission of monolayer transition metal dichalcogenides (1L TMDs). However, so far, the effective control of valley polarization degree in monolayer TMDs semiconductors is mostly achieved at liquid helium cryogenic temperature (4.2 K), with the requirements of high magnetic field and on‐resonance laser, which are of high cost and unwelcome for applications. To overcome this obstacle, it is depicted that by electrostatic and optical doping, even at temperatures far above liquid helium cryogenic temperature (80 K) and under off‐resonance laser excitation, a competitive valley polarization degree of monolayer WS2 can be achieved (more than threefold enhancement). The enhanced polarization is understood by a general doping dependent valley relaxation mechanism, which agrees well with the unified theory of carrier screening effects on intervalley scattering process. These results demonstrate that the tunability corresponds to an effective magnet field of ≈10 T at 4.2 K. This work not only serves as a reference to future valleytronic studies based on monolayer TMDs with various external or native carrier densities, but also provides an alternative approach toward enhanced polarization degree, which denotes an essential step toward practical valleytronic applications.

Enhancing and controlling valley magnetic response in MoS2/WS2 heterostructures by all-optical route

“…The investigation and control of the valley degree of freedom (DoF) are important topics in condensed matter physics and would give rise to new paradigms to encode and process information for future valleytronic and optoelectronic applications 1–4 . Two-dimensional (2D) transition metal dichalcogenides (TMDCs) with unique electronic band structure, such as direct band gap 5,6 , giant spin-orbit coupling (SOC), and entangled valley and spin DoF 7,8 , provide an unprecedented platform to manipulate the valley pseudospin through circularly polarized light excitation 9–12 and electric field as well 13–17 . Moreover, due to valley-contrasting Berry curvature and magnetic moment 8 , magnetic field offers an effective opportunity to engineer the valley DoF.…”

Enhanced valley polarization in WS$_2$/LaMnO$_3$ heterostructure

“…Besides, the double interlayer excitons in such TMD/ferromagnet heterostructures also verifies the existence of charge transfer from WS 2 to LMO substrate, which might enhance the valley polarization of exciton in monolayer WS 2 [24,25]. depicted by [4,20],…”

“…So far, the valley polarization of monolayer TMD reported is not high [12,13], which is mainly attributed to intervalley scattering process from the selectively pumped valley to the opposite one [14,15]. Several works have been reported to increase the valley polarization by using various methods, such as high magnetic field, low temperature, resonant excitation, optical or electrical doping and so on [4,5,[16][17][18][19][20][21]. Most methods require harsh conditions and the improvements are still not good enough.…”

Electrically Tunable and Dramatically Enhanced Valley‐Polarized Emission of Monolayer WS2 at Room Temperature with Plasmonic Archimedes Spiral Nanostructures

“…[56] Our work aims to tailor the degree of valley polarization by manipulating the intervalley scattering rate (τ v ) −1 via tuning the carrier doping. Noting that the valley polarization P DVP [57] is given by…”