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arXiv 1809.04562cond-mat.mes-hall
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MoSe $_2$ /WSe $_2$异质双层膜中的莫尔陷陷谷激子特征

Signatures of moiré-trapped valley excitons in MoSe$_2$/WSe$_2$ heterobilayers

Kyle L. Seyler, Pasqual Rivera, Hongyi Yu, Nathan P. Wilson, Essance L. Ray, David Mandrus, Jiaqiang Yan, Wang Yao, Xiaodong Xu

摘要:

在晶体固体中产生莫尔图案是操纵其电子性质的有力方法,这些电子性质从根本上受到周期性势场的影响。在2D材料中,具有超晶格势的莫尔图案可以通过垂直堆叠具有扭曲和/或有限晶格常数差的两层材料来形成。这种独特的方法导致了涌现的电子现象,包括分形量子霍尔效应,可调莫特绝缘体,和非常规的超导性。此外,理论预测了2D谷半导体中莫尔势对光激发的有趣影响,但这些特征尚未被实验检测到。在这里,我们报告的实验证据的层间谷激子被困在MoSe $_2$ /WSe $_2$异质双层膜中的莫尔电位。在低温下,我们观察到的光致发光附近的自由层间激子的能量,但超过100倍窄的线宽。发射极g因子在同一样品上是均匀的,并且在扭转角分别接近60°和0°的样品中仅取两个值,-15.9和6.7。的g-因子匹配的自由层间激子,这是由两个可能的谷配对配置之一。在接近20°的扭转角下,发射器变得两个数量级的调光器,但值得注意的是,它们具有与接近60°的异质双层相同的g因子。这与层间激子在21.8°扭转角附近的Umklapp复合一致。发射体表现出很强的圆极化,这意味着捕获势保持了三重旋转对称性。连同功率和激发能依赖性,所有证据都指向它们的起源,即层间激子被困在具有继承的谷对比物理学的平滑莫尔势中。

英文摘要:

The creation of moiré patterns in crystalline solids is a powerful approach to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In 2D materials, a moiré pattern with a superlattice potential can form by vertically stacking two layered materials with a twist and/or finite lattice constant difference. This unique approach has led to emergent electronic phenomena, including the fractal quantum Hall effect, tunable Mott insulators, and unconventional superconductivity. Furthermore, theory predicts intriguing effects on optical excitations by a moiré potential in 2D valley semiconductors, but these signatures have yet to be experimentally detected. Here, we report experimental evidence of interlayer valley excitons trapped in a moiré potential in MoSe$_2$/WSe$_2$ heterobilayers. At low temperatures, we observe photoluminescence near the free interlayer exciton energy but with over 100 times narrower linewidths. The emitter g-factors are homogeneous across the same sample and only take two values, -15.9 and 6.7, in samples with twisting angles near 60° and 0°, respectively. The g-factors match those of the free interlayer exciton, which is determined by one of two possible valley pairing configurations. At a twist angle near 20°, the emitters become two orders of magnitude dimmer, but remarkably, they possess the same g-factor as the heterobilayer near 60°. This is consistent with the Umklapp recombination of interlayer excitons near the commensurate 21.8° twist angle. The emitters exhibit strong circular polarization, which implies the preservation of three-fold rotation symmetry by the trapping potential. Together with the power and excitation energy dependence, all evidence points to their origin as interlayer excitons trapped in a smooth moiré potential with inherited valley-contrasting physics.

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