Signatures of moire-trapped valley excitons in MoSe2/WSe2 heterobilayers
Signatures of moire-trapped valley excitons in MoSe2/WSe2 heterobilayers
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DOI：
10.1038/s41586-019-0957-1
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发表时间：
2019-03-07
期刊：
影响因子：
64.8
通讯作者：
Xu, Xiaodong
中科院分区：
文献类型：
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作者：
Seyler, Kyle L.;Rivera, Pasqual;Xu, Xiaodong
结晶固体中莫尔条纹的形成可以用来操纵它们的电子性质，这些性质从根本上受到周期性势场的影响。在二维材料中，具有超晶格势的莫尔图案可以通过垂直堆叠具有扭曲和/或晶格常数差异的两层材料来形成。这种方法导致了电子现象，包括分形量子霍尔效应（1 - 3），可调莫特绝缘体（4，5）和非常规超导性（6）。此外，理论预测，二维谷半导体中的莫尔势可能会对光激发产生显著影响（7 - 9），但这些特征尚未在实验中检测到。在这里，我们报告的实验证据层间谷激子被困在一个莫尔电位在二硒化钼（MoSe 2）/二硒化钨（WSe 2）异质双层。在低温下，我们观察到的光致发光接近自由层间激子的能量，但线宽超过100倍窄（约100微电子伏）。发射器g因子在相同样品上是均匀的，并且在具有近似60度和0度的扭转角的样品中分别仅取两个值-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。在大约20度的扭转角下，发射器变得两个数量级的调光器;然而，它们在大约60度的扭转角下具有与异质双层相同的g因子。这与层间激子在相称的21.8度扭转角附近的umklapp复合一致（7）。对于给定的扭转角，发射体表现出相同螺旋度的强圆偏振，这表明捕获势保持三重旋转对称性。加上功率和激发能的特性依赖性，这些结果表明，所观察到的效果的起源是层间激子被困在一个光滑的莫尔电位与继承谷对比物理。这项工作提供了机会，通过扭转角的变化来控制二维莫尔光学。
The formation of moire patterns in crystalline solids can be used to manipulate their electronic properties, which are fundamentally influenced by periodic potential landscapes. In two-dimensional materials, a moire pattern with a superlattice potential can be formed by vertically stacking two layered materials with a twist and/or a difference in lattice constant. This approach has led to electronic phenomena including the fractal quantum Hall effect(1-3), tunable Mott insulators(4,5) and unconventional superconductivity(6). In addition, theory predicts that notable effects on optical excitations could result from a moire potential in two-dimensional valley semiconductors(7-9), but these signatures have not been detected experimentally. Here we report experimental evidence of interlayer valley excitons trapped in a moire potential in molybdenum diselenide (MoSe2)/tungsten diselenide (WSe2) heterobilayers. At low temperatures, we observe photoluminescence close to the free interlayer exciton energy but with linewidths over one hundred times narrower (around 100 microelectronvolts). The emitter g-factors are homogeneous across the same sample and take only two values, -15.9 and 6.7, in samples with approximate twist angles of 60 degrees and 0 degrees, respectively. The g-factors match those of the free interlayer exciton, which is determined by one of two possible valley-pairing configurations. At twist angles of approximately 20 degrees the emitters become two orders of magnitude dimmer; however, they possess the same g-factor as the heterobilayer at a twist angle of approximately 60 degrees. This is consistent with the umklapp recombination of interlayer excitons near the commensurate 21.8-degree twist angle(7). The emitters exhibit strong circular polarization of the same helicity for a given twist angle, which suggests that the trapping potential retains three-fold rotational symmetry. Together with a characteristic dependence on power and excitation energy, these results suggest that the origin of the observed effects is interlayer excitons trapped in a smooth moire potential with inherited valley-contrasting physics. This work presents opportunities to control two-dimensional moire optics through variation of the twist angle.