Valley Zeeman effect in elementary optical excitations of monolayer WSe2
Valley Zeeman effect in elementary optical excitations of monolayer WSe2
复制标题
DOI：
10.1038/nphys3203
复制
发表时间：
2015-02-01
期刊：
影响因子：
19.6
通讯作者：
Imamoglu, A.
中科院分区：
文献类型：
--
作者：
Srivastava, Ajit;Sidler, Meinrad;Imamoglu, A.
WSe2等过渡金属二卤化物的单层是一种二维直接带隙山谷半导体(1，2)，具有破坏反转对称性的有效蜂窝晶格结构。布里渊区的不等效谷可以用圆偏振光场来选择性地寻址，这表明磁光测量和操纵谷伪自旋自由度(6-8)是可能的。在这里，我们报道了这样的实验，它展示了山谷塞曼效应--利用外部磁场强烈各向异性地提升山谷赝旋自由度的简并性。用激子跃迁测量的谷分裂与用三带紧束缚模型(9)对+/-K谷的独立电子-空穴对计算的值有相当大的偏差。另一方面，我们表明，考虑到激子的强束缚性质的理论模型与实验观察到的分裂有很好的一致性。与激子相反，三子跃迁表现出出人意料的大山谷塞曼效应，这是在相同的框架下无法理解的，这暗示了对三子磁矩的不同贡献。我们的结果提出了利用单层过渡金属二卤化物中的磁场来控制谷自由度的可能性，或者在微腔(10)中观察与基本光激发强耦合的光子的拓扑态。
A monolayer of a transition metal dichalcogenide such as WSe2 is a two-dimensional direct-bandgap valley-semiconductor(1,2) having an effective honeycomb lattice structure with broken inversion symmetry. The inequivalent valleys in the Brillouin zone could be selectively addressed using circularly polarized light fields', suggesting the possibility for magneto-optical measurement and manipulation of the valley pseudospin degree of freedom(6-8). Here we report such experiments that demonstrate the valley Zeeman effect-strongly anisotropic lifting of the degeneracy of the valley pseudospin degree of freedom using an external magnetic field. The valley-splitting measured using the exciton transition deviates appreciably from values calculated using a three-band tight-binding model(9) for an independent electron-hole pair at +/- K valleys. We show, on the other hand, that a theoretical model taking into account the strongly bound nature of the exciton yields an excellent agreement with the experimentally observed splitting. In contrast to the exciton, the trion transition exhibits an unexpectedly large valley Zeeman effect that cannot be understood within the same framework, hinting at a different contribution to the trion magnetic moment. Our results raise the possibility of controlling the valley degree of freedom using magnetic fields in monolayer transition metal dichalcogenides or observing topological states of photons strongly coupled to elementary optical excitations in a microcavity(10).