Li Zhipeng, Wang Tianmeng, Lu Zhengguang, Khatoniar Mandeep, Lian Zhen, Meng Yuze, Blei Mark, Taniguchi Takashi, Watanabe Kenji, McGill Stephen A, Tongay Sefaattin, Menon Vinod M, Smirnov Dmitry, Shi Su-Fei
Department of Chemical and Biological Engineering , Rensselaer Polytechnic Institute , Troy , New York 12180 , United States.
National High Magnetic Field Lab , Tallahassee , Florida 32310 , United States.
Nano Lett. 2019 Oct 9;19(10):6886-6893. doi: 10.1021/acs.nanolett.9b02132. Epub 2019 Sep 9.
Spin-forbidden intravalley dark excitons in tungsten-based transition-metal dichalcogenides (TMDCs), because of their unique spin texture and long lifetime, have attracted intense research interest. Here, we show that we can control the dark exciton electrostatically by dressing it with one free electron or free hole, forming the dark trions. The existence of the dark trions is suggested by the unique magneto-photoluminescence spectroscopy pattern of the boron nitride (BN)-encapsulated monolayer WSe device at low temperature. The unambiguous evidence of the dark trions is further obtained by directly resolving the radiation pattern of the dark trions through back focal plane imaging. The dark trions possess a binding energy of ∼15 meV, and they inherit the long lifetime and large -factor from the dark exciton. Interestingly, under the out-of-plane magnetic field, dressing the dark exciton with one free electron or hole results in distinctively different valley polarization of the emitted photon, as a result of the different intervalley scattering mechanism for the electron and hole. Finally, the lifetime of the positive dark trion can be further tuned from ∼50 ps to ∼215 ps by controlling the gate voltage. The gate-tunable dark trions usher in new opportunities for excitonic optoelectronics and valleytronics.
基于钨的过渡金属二硫属化物（TMDCs）中的自旋禁戒谷内暗激子，因其独特的自旋纹理和长寿命，引起了广泛的研究兴趣。在此，我们表明可以通过用一个自由电子或自由空穴修饰暗激子来静电控制它，从而形成暗激子三重组。低温下氮化硼（BN）封装的单层WSe器件独特的磁光致发光光谱模式表明了暗激子三重组的存在。通过背焦平面成像直接解析暗激子三重组的辐射模式，进一步获得了暗激子三重组的明确证据。暗激子三重组具有约15 meV的结合能，并且继承了暗激子的长寿命和大因子。有趣的是，在面外磁场下，用一个自由电子或空穴修饰暗激子会导致发射光子的谷极化明显不同，这是由于电子和空穴的不同谷间散射机制所致。最后，通过控制栅极电压，正暗激子三重组的寿命可以从约50 ps进一步调谐到约215 ps。栅极可调谐暗激子三重组为激子光电子学和谷电子学带来了新的机遇。
