Ultrafast pseudospin quantum beats in multilayer WSe2 and MoSe2

Raiber, Simon; Faria Junior, Paulo E.; Falter, Dennis; Feldl, Simon; Marzena, Petter; Watanabe, Kenji; Taniguchi, Takashi; Fabian, Jaroslav; Schüller, Christian

doi:10.1038/s41467-022-32534-3

Cited by 9 publications

(7 citation statements)

References 77 publications

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“…As a result, the magnitudes of g X ns in BL are reduced with respect to ML. Furthermore, a stronger localisation of the 2s A state around the K point leads to the increase of their g-factor magnitudes, in agreement with previous theoretical and experimental findings [36,38]. Due to the different signs of valence and conduction Bloch states g-factors involved in IL A and IL B excitons, their g-factors are positive and exhibit a negative curvature.…”

Section: G-factors Of Exciton Ns Statessupporting

confidence: 90%

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Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe₂

et al. 2023

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Excitons in thin layers of semiconducting transition metal dichalcogenides are highly subject to the strongly modified Coulomb electron-hole interaction in these materials. Therefore, they do not follow the model system of a two-dimensional hydrogen atom. We investigate experimentally and theoretically excitonic properties in both the monolayer (ML) and the bilayer (BL) of MoSe2 encapsulated in hexagonal BN. The measured magnetic field evolutions of the reflectance contrast spectra of the MoSe2 ML and BL allow us to determine g-factors of intralayer A and B excitons, as well as the g-factors of the interlayer exciton. We explain the dependence of g-factors on the number of layers and excitation state can be explained using first principles calculations. Furthermore, we demonstrate that the experimentally measured ladder of excitonic s states in the ML can be reproduced using the k·p approach with the Rytova-Keldysh potential that describes the electron-hole interaction. In contrast, the analogous calculation for the BL case require taking into account the out-of-plane dielectric response of the MoSe2 BL.

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Section: G-factors Of Exciton Ns Statessupporting

confidence: 90%

“…Both possible changes (i.e. increase or decrease) of the corresponding g-factors of the s states are reported in the literature [8,9,[35][36][37][38]. In our opinion, the discrepancy between the experimental and theoretical values of the 2s A g-factor requires a more sophisticated analysis, which goes beyond the scope of this work.…”

Section: Resultsmentioning

confidence: 64%

Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe₂

et al. 2023

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“…In this section, we explore the spin and orbital degrees of freedom for the relevant band edges (indicated in Figure 1 g) at zero electric field and at the equilibrium interlayer distance. We follow recent first-principles developments, to compute the orbital angular momenta in monolayer TMDCs [ 64 , 65 , 66 , 67 ], which has also been successfully applied to investigate a variety of more complex TMDC-based systems and van der Waals heterostructures [ 27 , 53 , 57 , 80 , 85 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 ]. We do not aim to provide a detailed description of the methodology here, but briefly summarize the main points.…”

Section: Spin-valley Physics At the Band Edgesmentioning

confidence: 99%

Signatures of Electric Field and Layer Separation Effects on the Spin-Valley Physics of MoSe2/WSe2 Heterobilayers: From Energy Bands to Dipolar Excitons

Faria

Fabian

2023

Nanomaterials

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Multilayered van der Waals heterostructures based on transition metal dichalcogenides are suitable platforms on which to study interlayer (dipolar) excitons, in which electrons and holes are localized in different layers. Interestingly, these excitonic complexes exhibit pronounced valley Zeeman signatures, but how their spin-valley physics can be further altered due to external parameters—such as electric field and interlayer separation—remains largely unexplored. Here, we perform a systematic analysis of the spin-valley physics in MoSe2/WSe2 heterobilayers under the influence of an external electric field and changes of the interlayer separation. In particular, we analyze the spin (Sz) and orbital (Lz) degrees of freedom, and the symmetry properties of the relevant band edges (at K, Q, and Γ points) of high-symmetry stackings at 0° (R-type) and 60° (H-type) angles—the important building blocks present in moiré or atomically reconstructed structures. We reveal distinct hybridization signatures on the spin and the orbital degrees of freedom of low-energy bands, due to the wave function mixing between the layers, which are stacking-dependent, and can be further modified by electric field and interlayer distance variation. We find that H-type stackings favor large changes in the g-factors as a function of the electric field, e.g., from −5 to 3 in the valence bands of the Hhh stacking, because of the opposite orientation of Sz and Lz of the individual monolayers. For the low-energy dipolar excitons (direct and indirect in k-space), we quantify the electric dipole moments and polarizabilities, reflecting the layer delocalization of the constituent bands. Furthermore, our results show that direct dipolar excitons carry a robust valley Zeeman effect nearly independent of the electric field, but tunable by the interlayer distance, which can be rendered experimentally accessible via applied external pressure. For the momentum-indirect dipolar excitons, our symmetry analysis indicates that phonon-mediated optical processes can easily take place. In particular, for the indirect excitons with conduction bands at the Q point for H-type stackings, we find marked variations of the valley Zeeman (∼4) as a function of the electric field, which notably stands out from the other dipolar exciton species. Our analysis suggests that stronger signatures of the coupled spin-valley physics are favored in H-type stackings, which can be experimentally investigated in samples with twist angle close to 60°. In summary, our study provides fundamental microscopic insights into the spin-valley physics of van der Waals heterostructures, which are relevant to understanding the valley Zeeman splitting of dipolar excitonic complexes, and also intralayer excitons.

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“…Interestingly, the exciton g-factor depends only weakly on the band gap, while the band g-factors are indeed more sensitive to E g [42], as expected from conventional III-V semiconductors within the k.p framework [41,46]. While the valley Zeeman physics in intrinsic monolayers [42][43][44][45][47][48][49] and hetero/homo-bilayers [42,45,[50][51][52][53][54][55] is relatively well understood based on the recent ab initio developments, the influence of finite carrier density [56][57][58][59][60][61][62] (see also theoretical efforts in [63,64]) or the evolution of the (in-plane) spin and orbital degrees of freedom in multilayered van der Waals heterostructures [65] still require further work.…”

Section: Introductionmentioning

confidence: 99%

Proximity-enhanced valley Zeeman splitting at the WS₂/graphene interface

et al. 2023

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The valley Zeeman physics of excitons in monolayer transition metal dichalcogenides provides valuable insight into the spin and orbital degrees of freedom inherent to these materials. Being atomically-thin materials, these degrees of freedom can be influenced by the presence of adjacent layers, due to proximity interactions that arise from wave function overlap across the 2D interface. Here, we report 60 T magnetoreflection spectroscopy of the A- and B- excitons in monolayer WS$_2$, systematically encapsulated in monolayer graphene. While the observed variations of the valley Zeeman effect for the A- exciton are qualitatively in accord with expectations from the bandgap reduction and modification of the exciton binding energy due to the graphene-induced dielectric screening, the valley Zeeman effect for the B- exciton behaves markedly different. We investigate prototypical WS$_2$/graphene stacks employing first-principles calculations and find that the lower conduction band of WS$_2$ at the $K/K'$ valleys (the $CB^-$ band) is strongly influenced by the graphene layer on the orbital level. Specifically, our detailed microscopic analysis reveals that the conduction band at the $Q$ point of WS$_2$ mediates the coupling between $CB^-$ and graphene due to resonant energy conditions and strong coupling to the Dirac cone. This leads to variations in the valley Zeeman physics of the B- exciton, consistent with the experimental observations. Our results therefore expand the consequences of proximity effects in multilayer semiconductor stacks, showing that wave function hybridization can be a multi-step energetically resonant process, with different bands mediating the interlayer interactions. Such effects can be further exploited to resonantly engineer the spin-valley degrees of freedom in van der Waals and moiré heterostructures.

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Ultrafast pseudospin quantum beats in multilayer WSe2 and MoSe2

Cited by 9 publications

References 77 publications

Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe₂

Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe₂

Signatures of Electric Field and Layer Separation Effects on the Spin-Valley Physics of MoSe2/WSe2 Heterobilayers: From Energy Bands to Dipolar Excitons

Proximity-enhanced valley Zeeman splitting at the WS₂/graphene interface

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Ultrafast pseudospin quantum beats in multilayer WSe2 and MoSe2

Cited by 9 publications

References 77 publications

Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe2

Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe2

Signatures of Electric Field and Layer Separation Effects on the Spin-Valley Physics of MoSe2/WSe2 Heterobilayers: From Energy Bands to Dipolar Excitons

Proximity-enhanced valley Zeeman splitting at the WS2/graphene interface

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Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe₂

Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe₂

Proximity-enhanced valley Zeeman splitting at the WS₂/graphene interface