Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides
Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides
复制标题
原子薄钨二硫化物中对称变化和自旋谷耦合的光学特征
DOI：
10.1038/srep01608
复制
发表时间：
2013-04-11
影响因子：
4.6
通讯作者：
Cui, Xiaodong
中科院分区：
文献类型：
--
作者：
Zeng, Hualing;Liu, Gui-Bin;Cui, Xiaodong
我们报道了WS2和WSe2单层和多层膜的系统光学研究。二次谐波的产生效率随层数的增加呈现出明显的奇偶振荡，这与偶层(奇层)中反转对称性的存在(不存在)相一致。光致发光(PL)测量表明，多层膜上的间接带隙半导体与单层膜上的直接带隙半导体发生了交叉。所有样品的热发光峰(B)均位于突出的带边峰(A)上方的0.4 eV附近。A-B分裂的大小与膜的层数无关，与单分子膜中的自旋-谷耦合强度一致。从头算结果表明，这种与厚度无关的分裂模式是巨大的自旋谷耦合的直接结果，它完全抑制了K点附近价带边的层间跳跃，这是因为2H堆积顺序中层与层之间的自旋谷耦合的符号变化。
We report systematic optical studies of WS2 and WSe2 monolayers and multilayers. The efficiency of second harmonic generation shows a dramatic even-odd oscillation with the number of layers, consistent with the presence (absence) of inversion symmetry in even-layer (odd-layer). Photoluminescence (PL) measurements show the crossover from an indirect band gap semiconductor at multilayers to a direct-gap one at monolayers. A hot luminescence peak (B) is observed at similar to 0.4 eV above the prominent band edge peak (A) in all samples. The magnitude of A-B splitting is independent of the number of layers and coincides with the spin-valley coupling strength in monolayers. Ab initio calculations show that this thickness independent splitting pattern is a direct consequence of the giant spin-valley coupling which fully suppresses interlayer hopping at valence band edge near K points because of the sign change of the spin-valley coupling from layer to layer in the 2H stacking order.