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1. Long-range transport of 2D excitons with acoustic waves

   https://doi.org/10.1038/s41467-022-29042-9  

   Peng, Ruoming; Ripin, Adina; Ye, Yusen; Zhu, Jiayi; Wu, Changming; Lee, Seokhyeong; Li, Huan; Taniguchi, Takashi; Watanabe, Kenji; Cao, Ting; et al (December 2022, Nature Communications)

   Abstract Excitons are elementary optical excitation in semiconductors. The ability to manipulate and transport these quasiparticles would enable excitonic circuits and devices for quantum photonic technologies. Recently, interlayer excitons in 2D semiconductors have emerged as a promising candidate for engineering excitonic devices due to their long lifetime, large exciton binding energy, and gate tunability. However, the charge-neutral nature of the excitons leads to weak response to the in-plane electric field and thus inhibits transport beyond the diffusion length. Here, we demonstrate the directional transport of interlayer excitons in bilayer WSe 2 driven by the propagating potential traps induced by surface acoustic waves (SAW). We show that at 100 K, the SAW-driven excitonic transport is activated above a threshold acoustic power and reaches 20 μm, a distance at least ten times longer than the diffusion length and only limited by the device size. Temperature-dependent measurement reveals the transition from the diffusion-limited regime at low temperature to the acoustic field-driven regime at elevated temperature. Our work shows that acoustic waves are an effective, contact-free means to control exciton dynamics and transport, promising for realizing 2D materials-based excitonic devices such as exciton transistors, switches, and transducers up to room temperature. 

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2. Long-range spatial extension of exciton states in van der Waals heterostructure

   https://doi.org/10.1038/s41467-026-70218-4  

   Zhou, Zhiwen; Szwed, E A; Brunner, W J; Henstridge, H; Fowler-Gerace, L H; Butov, L V (March 2026, Nature Communications)

   Abstract Narrow lines in photoluminescence (PL) spectra of excitons are characteristic of low-dimensional semiconductors. These lines correspond to the emission of exciton states in local minima of a potential energy landscape formed by fluctuations of the local exciton environment in the heterostructure. The spatial extension of such states was in the nanometer range. In this work, we present studies of narrow lines in PL spectra of spatially indirect excitons (IXs) in a MoSe₂/WSe₂van der Waals heterostructure. The narrow lines vanish with increasing IX density. The disappearance of narrow lines correlates with the onset of IX transport, indicating that the narrow lines correspond to localized exciton states. The narrow lines extend over distances reaching several micrometers and over areas reaching ca. ten percent of the sample area. This macroscopic spatial extension of the exciton states, corresponding to the narrow lines, indicates a deviation of the exciton energy landscape from random potential and shows that the excitons are confined in moiré potential with a weak disorder. 

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3. Confinement of excited states in two-dimensional, in-plane, quantum heterostructures

   https://doi.org/10.1038/s41467-024-50653-x  

   Kim, Gwangwoo; Huet, Benjamin; Stevens, Christopher E; Jo, Kiyoung; Tsai, Jeng-Yuan; Bachu, Saiphaneendra; Leger, Meghan; Song, Seunguk; Rahaman, Mahfujur; Ma, Kyung Yeol; et al (December 2024, Nature Communications)

   Abstract Two-dimensional (2D) semiconductors are promising candidates for optoelectronic application and quantum information processes due to their inherent out-of-plane 2D confinement. In addition, they offer the possibility of achieving low-dimensional in-plane exciton confinement, similar to zero-dimensional quantum dots, with intriguing optical and electronic properties via strain or composition engineering. However, realizing such laterally confined 2D monolayers and systematically controlling size-dependent optical properties remain significant challenges. Here, we report the observation of lateral confinement of excitons in epitaxially grown in-plane MoSe₂quantum dots (~15-60 nm wide) inside a continuous matrix of WSe₂monolayer film via a sequential epitaxial growth process. Various optical spectroscopy techniques reveal the size-dependent exciton confinement in the MoSe₂monolayer quantum dots with exciton blue shift (12-40 meV) at a low temperature as compared to continuous monolayer MoSe₂. Finally, single-photon emission (g²(0) ~ 0.4) was also observed from the smallest dots at 1.6 K. Our study opens the door to compositionally engineered, tunable, in-plane quantum light sources in 2D semiconductors. 

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4. Phonon‐Dressed States of Dark Excitons in Transition Metal Dichalcogenides

   https://doi.org/10.1002/adom.202503833  

   Chand, Saroj B; Woods, John M; Quan, Jiamin; Mejia, Enrique; Adhikari, Ashok; Wang, Wei; Taniguchi, Takashi; Watanabe, Kenji; Alù, Andrea; Grosso, Gabriele (April 2026, Advanced Optical Materials)

   Electron–phonon interactions strongly influence exciton dynamics, enabling control at the nanoscale over light‐matter interactions and coherent phenomena for emerging quantum sensing applications. In transition metal dichalcogenides, momentum‐forbidden dark excitons occupy the energy ground state and exhibit exceptional sensitivity to their local environment. Here, we optically characterize these dark excitonic states in WS₂and WSe₂monolayers by tuning their band alignment through strain. We unveil their pronounced localization, extended lifetimes, and high linear polarization, signatures of strong exciton–phonon coupling and environmental responsiveness. Multiple distinct emission peaks are consistent with phonon‐dressed excitonic replicas with an estimated Huang‐Rhys factor of about 5. Density functional theory calculations, combined with measured strain‐dependent emission energies, constrain the relevant energy scales and suggest possible phonon‐assisted pathways underlying these phonon‐dressed states. Because replica energies, relative spectral weights, polarization axis, and lifetime respond to environmental factors such as local strain, dielectric environment, and phonon populations, these phonon‐dressed dark excitons provide a materials platform for exciton‐based nanoscale sensing and coherent control in 2D semiconductors. 

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5. Tunable exciton valley-pseudospin orders in moiré superlattices

   https://doi.org/10.1038/s41467-024-48725-z  

   Xiong, Richen; Brantly, Samuel L; Su, Kaixiang; Nie, Jacob H; Zhang, Zihan; Banerjee, Rounak; Ruddick, Hayley; Watanabe, Kenji; Taniguchi, Takashi; Tongay, Seth Ariel; et al (December 2024, Nature Communications)

   Abstract Excitons in two-dimensional (2D) semiconductors have offered an attractive platform for optoelectronic and valleytronic devices. Further realizations of correlated phases of excitons promise device concepts not possible in the single particle picture. Here we report tunable exciton “spin” orders in WSe₂/WS₂moiré superlattices. We find evidence of an in-plane (xy) order of exciton “spin”—here, valley pseudospin—around exciton fillingv_ex = 1, which strongly suppresses the out-of-plane “spin” polarization. Upon increasingv_exor applying a small magnetic field of ~10 mT, it transitions into an out-of-plane ferromagnetic (FM-z) spin order that spontaneously enhances the “spin” polarization, i.e., the circular helicity of emission light is higher than the excitation. The phase diagram is qualitatively captured by a spin-1/2 Bose–Hubbard model and is distinct from the fermion case. Our study paves the way for engineering exotic phases of matter from correlated spinor bosons, opening the door to a host of unconventional quantum devices. 

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