Speaker: Fanyao Qu, Professor, Institute of Physics, University of Brasilia, Brazil
Date: Dec. 20, 2018
Time: 4:00 pm
Location: Room 702, Quantum Hall, Block C, Zhixin Building, Central Campus
Sponsor: the School of Physics
Exploiting the “valley” degree of freedom to store and manipulate information is an emerging direction of condensed matter physics, and provides a novel paradigm for future electronics. Transition metal dichalcogenides have valley degree of freedom, which features optical selection rule and spin-valley locking, making them promising for valleytronics devices and quantum computation. For either application, a long valley polarization lifetime and controllabel valley degree of freedom are crucial. We theoretically investigate the valley dynamics and steady state emissions of multiexcitons, including bright and dark excitons as well as biexcitons formed by either one-bright and one dark excitons (XXd) or two bright excitons (XX) in monolayer WS2 subjected to a tilted magnetic field. We demonstrate that both brightened dark excitons and biexcitons exhibit large valley splittings; nevertheless, the former is twice as large as the latter. Besides, their magneto-photoluminecence (PL) display very strong valley anisotropy. Aside from magnitude of magnetic field, both the valley splitting and anisotropy of the multiexciton emissions can also be tuned by magnetic field geometric configuration. Remarkably, both magneto-PL intensity and the valley anisotropy of XX is strongly enhanced as the temperature rises. Therefore the long lifetime and large valley splitting of the dark exciton and XXd biexciton in monolayer WS2 make them promising for long-distance transport and macroscopic quantum state generations.
Prof. Fanyao Qu is currently professor of Physics Department at University of Brasilia. His main research interests include Electronic structure, photothermal, quantum transport and topological properties of two-dimensional materials and Van der Waals heterojunctions, spin and multi-exciton valley dynamics of Van der Waals heterojunctions, quantum information and nanodevice simulation and so on. He has published nearly 100 papers in mainstream physics journals such as Phys. Rev. Lett., Phys. Rev. B and Appl. Phys. Lett, and participated in the compilation of four monographs such as Quantum-dot Based Light-emitting Diodes. He has been invited to make reports at international conferences 19 times and has organized international conferences twice.
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Edited by Wei Zhen