Revealing the impact of strain in the optical properties of bubbles in monolayer MoSe<sub>2</sub>

Covre, Felipe; Faria, Paulo E.; Gordo, V. Orsi; Brito, C Serati de; Zhumagulov, Yaroslav V.; Teodoro, M. D.; Couto, O. D. D.; Misoguti, L; Pratavieira, Sebastião; Andrade, Marcelo B.; Christianen, Peter C. M.; Fabian, Jaroslav; Withers, Freddie; Gobato, Y. Galvão

doi:10.1039/d2nr00315e

Cited by 10 publications

(13 citation statements)

References 99 publications

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“…External factors that can alter the energetic landscape of such dipolar excitons, and consequently their photoluminescence or reflectance spectra, are beyond the scope of the present manuscript. Regarding the spin-valley physics and g-factors, previous studies focusing on intralayer excitons in monolayer TMDCs show that DFT calculations indeed provide a remarkable agreement to experimental data for pristine 110,111 and strained 85,94,95 cases. These intralayer excitons have larger conduction-to-valence band dipole matrix elements, larger electron-hole exchange contributions, and weaker dielectric screening when compared to interlayer excitons.…”

Section: Low-energy Dipolar Excitonssupporting

confidence: 58%

“…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%

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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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Section: Low-energy Dipolar Excitonssupporting

confidence: 58%

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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“…Experimental studies combining magneto-optics and strained TMDCs are rather scarce in the literature [114,115] and only investigate the tensile (positive) strain regime. For instance, Mitioglu et al [114] studied the A exciton g-factor at T = 4.2 K in WSe 2 monolayers under uniaxial strain by analyzing different samples (very likely with different doping levels, since the exciton/trion ratio also changes).…”

Section: Direct Excitons At the K-valleys: G-factor Renormalization A...mentioning

confidence: 99%

“…This uniaxial strain introduces a splitting of the exciton peak, yielding two distinct g-factors, both less negative when compared to nominally unstrained values. Covre et al [115] studied the A exciton g-factor at T = 4 K in a MoSe 2 monolayer bubble with non-uniform strain regions, in which the carrier concentration and the dielectric environment were also changing. They observed that the A exciton g-factor increases its magnitude but to a value larger than the theoretical calculations, suggesting a strong influence of the other effects present in the sample.…”

Section: Direct Excitons At the K-valleys: G-factor Renormalization A...mentioning

confidence: 99%

First-principles insights into the spin-valley physics of strained transition metal dichalcogenides monolayers

et al. 2022

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Transition metal dichalcogenides (TMDCs) are ideal candidates to explore the manifestation of spin-valley physics under external stimuli. In this study, we investigate the influence of strain on the spin and orbital angular momenta, effective g-factors, and Berry curvatures of several monolayer TMDCs (Mo and W based) using a full ab initio approach. At the K-valleys, we find a surprising decrease of the conduction band spin expectation value for compressive strain, consequently increasing the dipole strength of the dark exciton by more than one order of magnitude (for ∼ 1 % – 2 % strain variation). We also predict the behavior of direct excitons g-factors under strain: tensile (compressive) strain increases (decreases) the absolute value of g-factors. Strain variations of ∼1% modify the bright (A and B) excitons g-factors by ∼0.3 (0.2) for W (Mo) based compounds and the dark exciton g-factors by ∼0.5 (0.3) for W (Mo) compounds. Our predictions could be directly visualized in magneto-optical experiments in strained samples at low temperature. Additionally, our calculations strongly suggest that strain effects are one of the possible causes of g-factor fluctuations observed experimentally. By comparing the different TMDC compounds, we reveal the role of spin–orbit coupling (SOC): the stronger the SOC, the more sensitive are the spin-valley features under applied strain. Consequently, monolayer WSe2 is a formidable candidate to explore the role of strain on the spin-valley physics. We complete our analysis by considering the side valleys, Γ and Q points, and by investigating the influence of strain in the Berry curvature. In the broader context of valley- and strain-tronics, our study provides fundamental microscopic insights into the role of strain in the spin-valley physics of TMDCs, which are relevant to interpret experimental data in monolayer TMDCs as well as TMDC-based van der Waals heterostructures.

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“…The electronic quality of TMDs depends considerably on the incorporation of high-quality dielectric materials that possess a low defect density as well as being atomically smooth and uniform. 42,[158][159][160] Previous studies investigated the electrical and optical properties of FET-based vdWHs with talc as a dielectric material for surface protection. 41,42 Although these investigations (combination of phyllosilicates and TMDs) are at their early stages compared to hBN-based TMDs vdWHs, there are great opportunities which include optimization of sample preparation and the use of several other phyllosilicate materials.…”

Section: Electronic and Optoelectronic Applicationsmentioning

confidence: 99%

Phyllosilicates as earth-abundant layered materials for electronics and optoelectronics: Prospects and challenges in their ultrathin limit

Barcelos,

de Oliveira,

Schleder

et al. 2023

Journal of Applied Physics

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Phyllosilicate minerals are an emerging class of naturally occurring layered insulators with large bandgap energy that have gained attention from the scientific community. This class of lamellar materials has been recently explored at the ultrathin two-dimensional level due to their specific mechanical, electrical, magnetic, and optoelectronic properties, which are crucial for engineering novel devices (including heterostructures). Due to these properties, phyllosilicate minerals can be considered promising low-cost nanomaterials for future applications. In this Perspective article, we will present relevant features of these materials for their use in potential 2D-based electronic and optoelectronic applications, also discussing some of the major challenges in working with them.

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Revealing the impact of strain in the optical properties of bubbles in monolayer MoSe₂

Abstract: Strain plays an important role for the optical properties of monolayer transition metal dichalcogenides (TMDCs). Here, we investigate strain effects in a monolayer MoSe2 sample with a large bubble region...

Cited by 10 publications

References 99 publications

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

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

First-principles insights into the spin-valley physics of strained transition metal dichalcogenides monolayers

Phyllosilicates as earth-abundant layered materials for electronics and optoelectronics: Prospects and challenges in their ultrathin limit

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Revealing the impact of strain in the optical properties of bubbles in monolayer MoSe2

Abstract: Strain plays an important role for the optical properties of monolayer transition metal dichalcogenides (TMDCs). Here, we investigate strain effects in a monolayer MoSe2 sample with a large bubble region...

Cited by 10 publications

References 99 publications

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

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

First-principles insights into the spin-valley physics of strained transition metal dichalcogenides monolayers

Phyllosilicates as earth-abundant layered materials for electronics and optoelectronics: Prospects and challenges in their ultrathin limit

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Revealing the impact of strain in the optical properties of bubbles in monolayer MoSe₂