Long-Lived Hole Spin/Valley Polarization Probed by Kerr Rotation in Monolayer WSe₂

Abstract

Time-resolved Kerr rotation and photoluminescence measurements are performed on MOCVD-grown monolayer tungsten diselenide (WSe2). We observe a surprisingly long-lived Kerr rotation signal (∼80 ns) at 10 K, which is attributed to spin/valley polarization of the resident holes. This polarization is robust to transverse magnetic field (up to 0.3 T). Wavelength-dependent measurements reveal that only excitation near the free exciton energy generates this long-lived spin/valley polarization.

Opto-Valleytronic Spin Injection in Monolayer MoS2/Few-Layer Graphene Hybrid Spin Valves

“…8,9 Materials such as monolayer WSe 2 , with longer spin/valley lifetimes, may prove to be useful for improving the optical spin injection efficiency. [10][11][12] …”

“…TMDs have strong spin-orbit coupling due to the heavy metal atom and lack inversion symmetry in monolayer form, the combination of which allows complete simultaneous valley and spin polarization through absorption of circularly polarized light [8][9][10][11][12][13][14] . This originates from the valley-dependent optical selection rules of monolayer MoS 2 , where absorption of circularly polarized σ+ (σ-) photons excites electrons only in the K (K " ) valley.…”

“…Graphene exhibits room temperature spin diffusion length of up to tens of microns, substantially longer than conventional metals or semiconductors (<1 micron) [1][2][3][4] . However, graphene's lack of spin-dependent optical selection rules has made opto-spintronic functionality impossible, a substantial limitation for graphene.Fortunately, monolayer MoS 2 and related semiconducting transition metal dichalcogenides (TMDs) exhibit favorable characteristics for nanoscale opto-valleytronic and opto-spintronic applications [5][6][7] .TMDs have strong spin-orbit coupling due to the heavy metal atom and lack inversion symmetry in monolayer form, the combination of which allows complete simultaneous valley and spin polarization through absorption of circularly polarized light [8][9][10][11][12][13][14] . This originates from the valley-dependent optical selection rules of monolayer MoS 2 , where absorption of circularly polarized σ+ (σ-) photons excites electrons only in the K (K " ) valley.…”

Gate-Controlled Spin-Valley Locking of Resident Carriers in WSe2 Monolayers

“…Compared to typical CVD-grown WSe 2 , WS 2 , or MoS 2 , exfoliated WSe 2 exhibits fewer defects and much cleaner optical spectra. Of particular importance, and in contrast to earlier studies of resident carrier dynamics [18][19][20][21], the neutral (X 0 ) and charged exciton (X ± ) transitions are spectrally resolved and can be probed separately. A gate voltage V G tunes between n-type and p-type regimes, as confirmed in Figs.…”

Defect Structure of Localized Excitons in a WSe2 Monolayer

“…This p-type doping provides a natural route to fabricating a p-n junction based on lateral heterostructure [14,16]. Moreover, in conjunction with giant spin-orbit splitting and spin-valley locking at the valence band, p-type doping facilitates the manipulation of valley coherence for a more extended time to 1-10 ns [17,18], in comparison to ∼10 ps with n-type doping [19]. More interestingly, when the WSe 2 monolayer is cooled below ∼10 K, the defectrelated localized exciton emissions behave as single quantum emitters (SQEs) [20][21][22][23], which are essential for quantum information processing [9].…”