Temel Kavramlar
Uni-axial strain applied to molybdenum disulfide (MoS2) monolayers leads to diversified band dispersions of bright, gray, and dark excitons, impacting their optical properties and diffusion behavior, as revealed by first-principles calculations.
Özet
Bibliographic Information: Shih, C.-H.; Peng, G.-H.; Lo, P.-Y.; Li, W.-H.; Xu, M.-L.; Chien, C.-H.; Cheng, S.-J. Signatures of valley drift in the diversified band dispersions of bright, gray, and dark excitons in MoS2 monolayers under uni-axial strains. arXiv, 2024, 2410.03209.
Research Objective: This study investigates the impact of uni-axial strain on the excitonic properties of molybdenum disulfide (MoS2) monolayers using first-principles calculations based on the Bethe-Salpeter equation (BSE).
Methodology: The researchers employed density functional theory (DFT) to calculate the electronic band structure of strained MoS2 monolayers. They then used these results to solve the BSE and obtain the excitonic fine structures and band dispersions for different types of excitons (bright, gray, and dark) under varying uni-axial strain conditions.
Key Findings: The study reveals that uni-axial strain significantly affects the band dispersions of excitons in MoS2 monolayers. While bright exciton dispersions remain relatively insensitive to strain, gray exciton masses decrease, and dark exciton dispersions transform into a Mexican-hat-like profile, exhibiting negative effective mass and strain-activated brightness. These changes are attributed to the interplay between strain-induced valley drift and electron-hole exchange interactions.
Main Conclusions: The authors conclude that uni-axial strain can be used to manipulate the optical and transport properties of different exciton types in MoS2 monolayers. The diversified band dispersions result in distinct exciton diffusivities and angle-resolved optical patterns, suggesting potential applications in spatially resolving different exciton species.
Significance: This research provides valuable insights into the strain-engineering of excitonic properties in 2D materials, paving the way for novel optoelectronic and valleytronic devices.
Limitations and Future Research: The study focuses on MoS2 monolayers, and further research is needed to explore the strain-dependent excitonic properties in other TMD materials. Experimental verification of the predicted optical and transport characteristics is crucial for future device applications.
İstatistikler
Applying a tensile uni-axial strain to a MoS2 monolayer increases its energy gap, transitioning from an intra-valley to an inter-valley indirect gap.
The calculated drift of the conduction valley under 5% tensile strain is 0.091˚A−1, while the valence valley drifts by 0.074˚A−1.
The unstrained MoS2 monolayer exhibits a bright exciton-dark exciton splitting of 14 meV.
The effective mass of the gray exciton along the strain axis drops from 1.455m0 to 0.125m0 under 5% tensile strain.
The dark exciton band exhibits a sign-reversed effective mass of -0.150m0 at the gamma point under 5% tensile strain.
The critical strain for the emergence of the Mexican-hat-like dispersion in the dark exciton band is approximately 1.7%.
Alıntılar
"The unequal momentum VDs of conduction and valence bands implies the possible momentum shift of exciton ground states and the strain-reshaped exciton band structures."
"In contrast to spin-allowed BXs, our first principles studies reveal that an imposed uni-axial stress directly impacts the spin-forbidden exciton states in both the band dispersions as well as the optical selection rules."
"This suggests the emergent importance of DX in nano-optics based on strained 2D materials."
"The predicted diversification in the effective masses of exciton reveals the possibility to spatially resolve the BX, GX, and DX in exciton transport experiments by means of imposing an uni-axial strain to a TMD-ML."