Giant Valley-Zeeman Splitting from Spin-Singlet and Spin-Triplet Interlayer Excitons in WSe₂/MoSe₂ Heterostructure

Abstract

Transition metal dichalcogenides (TMDCs) heterostructure with a type II alignment hosts unique interlayer excitons with the possibility of spin-triplet and spin-singlet states. However, the associated spectroscopy signatures remain elusive, strongly hindering the understanding of the Moiré potential modulation of the interlayer exciton. In this work, we unambiguously identify the spin-singlet and spin-triplet interlayer excitons in the WSe2/MoSe2 hetero-bilayer with a 60-degree twist angle through the gate-and magnetic field-dependent photoluminescence spectroscopy. Both the singlet and triplet interlayer excitons show giant valley-Zeeman splitting between the K and K' valleys, a result of the large Landé g-factor of the singlet interlayer exciton and triplet interlayer exciton, which are experimentally determined to be ~ 10.7 and ~ 15.2, respectively, in good agreement with theoretical expectation. The PL from the singlet and triplet interlayer excitons show opposite helicities, determined by the atomic registry. Helicity-resolved photoluminescence excitation (PLE) spectroscopy study shows that both singlet and triplet interlayer excitons are highly valley-polarized at the resonant excitation, with the valley polarization of the singlet interlayer exciton approaches unity at ~ 20 K. The highly valley-polarized singlet and triplet interlayer excitons with giant valley-Zeeman splitting inspire future applications in spintronics and valleytronics.

Moiré excitons in MoSe2-WSe2 heterobilayers and heterotrilayers

“…4a, b (−6.2 ± 0.8, −4.2 ± 0.8, and −5.5 ± 0.8) are consistent with previous studies of aligned MoSe 2 -WSe 2 heterostructures in R-type registry with absolute values in the range from 6.1 to 8.5 15,24,28 . They clearly contrast the interlayer exciton g-factor values between 15 and 16 in HBLs of Htype registry 15,26,29,53 . For the respective KK interlayer excitons in R-type HBLs, our calculations (Supplementary Note 7) predict an absolute g-factor value close to 6 and opposite signs for the degrees of circular polarization in AA and A′B′ stackings (with negative and positive P C , respectively), in agreement with a similar theoretical analysis of interlayer exciton g-factor values and signs 54,55 .…”

“…At each heterostack site, the overall multi-peak PL structure of HBL and HTL is mostly preserved upon the variation in the gate voltage (Supplementary Note 1) and excitation power down to 300 nW (Supplementary Note 3). Consistent with finite twist angle, the multi-peak PL of the HBL below 1.40 eV, with a peak separation of 30 meV between the two highest energy peaks and 15 meV between other consecutive peaks (Supplementary Note 3), is reminiscent of rich MoSe 2 -WSe 2 moiré spectral features 16 rather than of simple spectra from aligned HBLs [24][25][26][27][28][29] . Remarkably, the HTL PL, with a similar peak spacing of 15 meV, is strikingly similar to the cryogenic PL from native bilayer WSe 2 43 (Supplementary Note 4).…”

“…Despite numerous experimental and theoretical studies of MoSe 2 -WSe 2 HBLs, the origin of the lowestenergy PL remains a subject of debate 22 . While the majority of experimental studies interpret the HBL emission in terms of zeromomentum interlayer excitons with K or K 0 valley electrons and holes in MoSe 2 and WSe 2 15,16,19,21,[23][24][25][26][27][28][29] , others invoke excitons built from hybridized HBL conduction band states at Q pockets [30][31][32] , located roughly halfway between the center of the first Brillouin zone at Γ and K or K 0 valleys. Band structure calculations indeed suggest that hybridization of states near Q conduction band and Γ valence band of MoSe 2 and WSe 2 gives rise to strong energy renormalization upon HBL formation 2,33,34 which might turn either QK or QΓ interlayer excitons, composed of electrons at Q and holes at K or Γ, into the lowest-energy states.…”

Routing valley exciton emission of a WS2 monolayer via delocalized Bloch modes of in-plane inversion-symmetry-broken photonic crystal slabs

“…The emergence of two-dimensional transition metal dichalcogenides (TMDCs) has attracted tremendous interest for their possible applications in valleytronics [1][2][3][4][5][6][7][8][9][10][11][12] . Due to the broken inversion symmetry in TMDCs, two types of degenerate yet inequivalent valleys (labelled K and K' valleys) appear at the corners of the first Brillouin zone, as shown in Fig.…”

Interlayer-Exciton Based Nonvolatile Valleytronic Memory

“…The IX emission peak shows a redshift and the emission intensity is enhanced with the decrease of V g , and vice versa. The redshift of the IX emission peak with V g can be ascribed to the Stark effect 7,19 , which is further veri ed by the opposite shift trend of the IX emission peak in the devices with stacking order inversed ( Fig. S1).…”