Strain tunable interlayer and intralayer excitons in vertically stacked MoSe2/WSe2 heterobilayers

Abstract

Recently, interlayer and intralayer excitons in transition metal dichalcogenide heterobilayers have been studied both experimentally and theoretically. In spite of a growing interest, these layer-resolved excitons in the presence of external stimuli, such as strain, remain not fully understood. Here, using density-functional theory calculations with many-body effects, we explore the excitonic properties of vertically stacked MoSe2/WSe2 heterobilayer in the presence of in-plane biaxial strain of up to 5%. We calculate the strain dependence of exciton absorption spectrum, oscillator strength, wave function, and binding energy by solving the Bethe–Salpeter equation on top of the standard GW approach. We identify the interlayer and intralayer excitons by analyzing their electron-hole weights and spatial wave functions. We show that with the increase in strain magnitude, the absorption spectrum of the interlayer and intralayer excitons is red-shifted and re-ordered, and the binding energies of these layer-resolved excitons decrease monotonically and almost linearly. We derive the sensitivity of exciton binding energy to the applied strain and find that the intralayer excitons are more sensitive to strain than the interlayer excitons. For instance, a sensitivity of −7.9 meV/% is derived for the intra-MoSe2-layer excitons, which is followed by −7.4 meV/% for the intra-WSe2-layer excitons, and by −4.2 meV/% for the interlayer excitons. Our results indicate that interlayer and intralayer excitons in vertically stacked MoSe2/WSe2 heterobilayer are efficiently tunable by in-plane biaxial strain.

Anomalous Interlayer Exciton Diffusion in WS2/WSe2 Moiré Heterostructure

“…25 Furthermore, a trapping/detrapping process, which is a temperature-activated mechanism where thermal energy allows the exciton to hop across the moirépotential wells, has been proposed for a MoSe 2 /WSe 2 heterostructure at various twist angles. 26 Our observations of IX diffusion cannot be explained by such a model alone. For that reason, we consider the role of phonons, specifically of moire-induced phonons also known as phasons, 15 that are still experimentally unexplored.…”

“…Our findings go beyond the classical Arrhenius model of thermally activated exciton transport involving a simple fixed potential landscape that have been reported in previous works where exciton diffusion is negligible at low temperatures (below 100 K). 25,26,30 Instead, we find that below 100 K excitons can explore the system, despite being fully trapped inside deep moirépotentials. An accurate model describing the moireṕ otential landscape is also provided, matching the energy barrier obtained from temperature-dependent diffusion measurements.…”

“…Such an exponential behavior is expected when considering a simple moire-trap picture. 25,26,30 Once formed, the IXs are affected by the presence of the moireṕ otential landscape and are trapped in its local minima. However, if enough thermal energy is provided and the activation barrier is overcome, the IX can diffuse faster, reaching a value comparable with the one of intralayer excitons of an isolated monolayer where the moirépotential is not present (Figure S5).…”

Editorial: Theoretical study of two-dimensional materials for photocatalysis and photovoltaics

“…These materials are distinguished by their unique physical and chemical properties, making them highly suitable for a wide range of applications in optoelectronics, thermoelectrics, photovoltaics, and catalysis. Furthermore, novel 2D material prediction ( Ren et al, 2022a ), strain engineering ( Li et al, 2023 ), adsorption ( Ren et al, 2022b ), doping ( Chen et al, 2024 ), defect ( Luo et al, 2023 ), size effects ( Ren et al, 2023 ), and the application of external electric fields ( Sun et al, 2017 ) have proven to be effective approaches to further expand the applications of 2D materials.…”