应变驱动的'正弦'谷控制的混合Γ-K激子
Strain-Driven "Sinusoidal" Valley Control of Hybridized $Γ-\mathrm{K}$ Excitons
AI总结：
该研究通过统一框架揭示了应变驱动下混合Γ-K激子的动态机制，提出了一种连续可调的谷调节器，为谷电子学技术的发展提供了新思路。
摘要：
在单层WS₂中，双轴应变下动量间接Γ-K激子的光电发光（PL）最近被Blundo等人[Phys. Rev. Lett. 129, 067402 (2022)]观测到，但其微观起源仍不清楚。本文发展了一个统一的框架，能够重现测量的PL并揭示其基本激子机制。我们发现：(i) PL来源于真正混合的直接-间接激子本征态，而不是名义上混合但具有固定主导特征的物种；(ii) 直接激子通过一个此前未被认识的两步路径转化为间接激子——交换相互作用驱动的激子转移后跟随着自旋翻转；(iii) 一种更高能级的间接激子，此前研究中未出现，作为这种转换的中介。除了解释实验外，我们的理论预测了一种令人惊叹的应变驱动的'正弦'谷响应，提供了一个连续可调的谷调节器，远远超过了二元控制方案。这种应变工程直接-间接激子动态的统一图景引入了操控长寿命谷自由度的新范式，开辟了通往可编程谷赝自旋工程和下一代谷电子量子技术的道路。
英文摘要：
The photoluminescence (PL) of momentum-indirect $\rm Γ- K$ excitons in monolayer WS$_2$ under biaxial strain was recently observed by Blundo et al. [Phys. Rev. Lett. 129, 067402 (2022)], yet its microscopic origin remains elusive. Here we develop a unified framework that reproduces the measured PL and reveals its fundamental excitonic mechanism. We reveal that: (i) the PL originates from genuinely hybridized direct-indirect excitonic eigenstates, rather than nominally mixed species with fixed dominant character; (ii) the direct exciton converts into the indirect one via a previously unrecognized two-step pathway -- exchange-interaction-driven exciton transfer followed by a spin flip; and (iii) a higher-energy indirect exciton, absent from prior studies, acts as a crucial intermediate mediating this conversion. Beyond explaining experiment, our theory predicts a striking strain-driven "sinusoidal'' valley response, furnishing a continuously tunable valley dial that far exceeds binary control schemes. This unified picture of strain-engineered direct-indirect exciton dynamics introduces a new paradigm for manipulating long-lived valley degrees of freedom, opening a pathway toward programmable valley pseudospin engineering and next-generation valleytronic quantum technologies.
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