arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2005.05724cond-mat.mes-hall
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过渡金属二硫族化合物中声子辅助激子和三电子转换效率

Phonon-assisted exciton and trion conversion efficiency in transition metal Dichalcogenides

Sabrine Ayari, Sihem Jaziri, Robson Ferreira, Gerald Bastard

摘要:

光致发光光谱表明,单层过渡金属二硫属化物(MLTMDC)具有带电激子结合能,与光学声子的能量非常相似。这种神秘的巧合提供了机会,调查trion,激子和声子之间的多体相互作用,并导致有效的激子反斯托克斯过程的激光制冷和能量收集的潜力。在这项研究中,我们表明,在WSe 2材料中,trion结合能匹配两个声子模式,outofplane HP和in-plane LO模式。在这方面,使用费米黄金法则结合有效质量近似,我们研究了激子和trion之间的人口转移率,介导的单个声子。我们表明,虽然两个声子模式的上转换过程中的绝对重要性强烈依赖于实验条件,如温度和介电环境(基板),这两种模式导致的时间尺度上的上转换过程在几皮秒到亚纳秒的范围内,与最近的实验结果一致。在我们的研究中,还研究了共轭过程,作为温度和电子密度的函数。我们证明了激子到氚子的下转换过程在低电子密度和高温下是不可能的,而在低温和电子密度下,下转换过程急剧增加,达到几皮秒的时间尺度。最后,我们的研究结果表明,转换过程发生更迅速地在示范性单层的铼基二硫属化物(MoSe 2和MoTe 2)比钨二硫属化物。

英文摘要:

Photoluminescence spectra, shows that monolayer Transition-metal dichalcogenides (MLTMDCs), possess charged exciton binding energies, conspicuously similar to the energy of optical phonons. This enigmatic coincidence has offered opportunities to investigate many-body interactions between trion, exciton and phonon and led to efficient excitonic anti-Stokes processes with the potential for laser refrigeration and energy harvesting. In this study, we show that in WSe2 materials, the trion binding energy matches two phonon modes, the outofplane HP and the in-plane LO mode. In this respect, using the Fermi golden rule together with the effective mass approximation, we investigate the rate of the population transfers between exciton and trion, mediated by a single phonon. We demonstrate that, while the absolute importance of the two phonon modes on the upconversion process strongly depend on the experimental conditions such as the temperature and the dielectric environment (substrate), both modes lead to an up-conversion process on time scales in the range of few picoseconds to sub-nanosecond, consistent with recents experimental findings. The conjugate process is also investigated in our study, as a function of temperature and electron density . We prove that exciton to trion down-conversion process is very unlikely at low electron density and high temperature while it increases dramatically to reach few picoseconds time scale at low temperature and for electron density . Finally, our results show that conversion process occurs more rapidly in exemplary monolayer molybdenum-based dichalcogenides (MoSe2 and MoTe2) than tungsten dichalcogenides .

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