Hidden valley dynamics behind vanishing circular polarization in moiré excitons
Abstract
Optically addressable valley degrees of freedom in transition-metal dichalcogenide heterostructures provide a powerful platform for valleytronic and quantum-optical functionalities. In moiré superlattices, interlayer excitons inherit valley-contrasting optical selection rules while acquiring long lifetimes, electric dipoles, and site-dependent optical responses. However, because conventional measurements typically probe time-integrated valley polarization, the dynamical origin of vanishing polarization has remained elusive. Here, we show that a nearly zero steady-state valley polarization in electrically tunable moiré excitons does not necessarily indicate fast valley relaxation. Helicity-resolved time-resolved photoluminescence reveals a temporal crossing between co- and cross-circularly polarized emission, indicating that helicity-opposite dynamical components coexist and compensate after time integration. A minimal two-channel model, representing A-like and B-like moiré emission channels with opposite optical selection rules and distinct effective decay/depolarization rates, reproduces the observed helicity crossing without invoking a single rapid valley relaxation process. Furthermore, two-dimensional gate-field maps show that the crossing time evolves systematically with electrostatic tuning, demonstrating that the hidden valley dynamics are electrically controllable. These results show that time-integrated circular polarization can give a false-negative indication of valley polarization in multichannel valley emitters.
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BibTeX
@misc{urano2026hidden,
title = {{Hidden valley dynamics behind vanishing circular polarization in moiré excitons}},
author = {Yuto Urano and Lata Chouhan and Nurul Fariha Ahmad and Kenji Watanabe and Takashi Taniguchi and Daichi Kozawa and Ryo Kitaura},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.27963},
eprint = {2606.27963},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.27963},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Hidden valley dynamics behind vanishing circular polarization in moiré excitons
AU - Yuto Urano
AU - Lata Chouhan
AU - Nurul Fariha Ahmad
AU - Kenji Watanabe
AU - Takashi Taniguchi
AU - Daichi Kozawa
AU - Ryo Kitaura
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2606.27963
UR - https://arxiv.org/abs/2606.27963
AB - Optically addressable valley degrees of freedom in transition-metal dichalcogenide heterostructures provide a powerful platform for valleytronic and quantum-optical functionalities. In moiré superlattices, interlayer excitons inherit valley-contrasting optical selection rules while acquiring long lifetimes, electric dipoles, and site-dependent optical responses. However, because conventional measurements typically probe time-integrated valley polarization, the dynamical origin of vanishing polarization has remained elusive. Here, we show that a nearly zero steady-state valley polarization in electrically tunable moiré excitons does not necessarily indicate fast valley relaxation. Helicity-resolved time-resolved photoluminescence reveals a temporal crossing between co- and cross-circularly polarized emission, indicating that helicity-opposite dynamical components coexist and compensate after time integration. A minimal two-channel model, representing A-like and B-like moiré emission channels with opposite optical selection rules and distinct effective decay/depolarization rates, reproduces the observed helicity crossing without invoking a single rapid valley relaxation process. Furthermore, two-dimensional gate-field maps show that the crossing time evolves systematically with electrostatic tuning, demonstrating that the hidden valley dynamics are electrically controllable. These results show that time-integrated circular polarization can give a false-negative indication of valley polarization in multichannel valley emitters.
ER -