Many-Body Effects in Valleytronics: Direct Measurement of Valley Lifetimes in Single-Layer MoS2
Many-Body Effects in Valleytronics: Direct Measurement of Valley Lifetimes in Single-Layer MoS2
复制标题
DOI：
10.1021/nl403742j
复制
发表时间：
2014-01-01
期刊：
影响因子：
10.8
通讯作者：
Gundogdu, Kenan
中科院分区：
文献类型：
--
作者：
Mai, Cong;Barrette, Andrew;Gundogdu, Kenan
单层MoS2是新兴的“谷电子学”领域的理想材料，其中电荷载流子动量可以通过光激发进行精细控制。这个系统也被认为表现出强的多体相互作用，如通过紧密束缚的激子和trions所观察到的。在这里，我们报告直接测量的山谷弛豫动力学在单层二硫化钼，通过使用超快瞬态吸收光谱。我们的结果表明，强库仑相互作用显着影响山谷种群动态。圆偏振光的初始激发在K谷内产生电子空穴对。这些激子相干耦合到暗谷间激子态，这有利于快速电子谷去极化。由于价带自旋态的非简并性，空穴谷弛豫延迟高达约10 ps。谷间双激子的形成揭示了空穴谷弛豫动力学。我们观察到，双激子形成的结合能比传统半导体大一个数量级以上。这些测量为2D半导体中的谷特定过程提供了重要的见解。因此，它们可以用来建议设计能够控制谷极化的半导体材料的路线。
Single layer MoS2 is an ideal material for the emerging field of "valleytronics" in which charge carrier momentum can be finely controlled by optical excitation. This system is also known to exhibit strong many-body interactions as observed by tightly bound excitons and trions. Here we report direct measurements of valley relaxation dynamics in single layer MoS2, by using ultrafast transient absorption spectroscopy. Our results show that strong Coulomb interactions significantly impact valley population dynamics. Initial excitation by circularly polarized light creates electron-hole pairs within the K-valley. These excitons coherently couple to dark intervalley excitonic states, which facilitate fast electron valley depolarization. Hole valley relaxation is delayed up to about 10 ps due to nondegeneracy of the valence band spin states. Intervalley biexciton formation reveals the hole valley relaxation dynamics. We observe that biexcitons form with more than an order of magnitude larger binding energy compared to conventional semiconductors. These measurements provide significant insight into valley specific processes in 2D semiconductors. Hence they could be used to suggest routes to design semiconducting materials that enable control of valley polarization.