Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2
Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2
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DOI：
10.1038/nphys3419
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发表时间：
2015-10-01
期刊：
影响因子：
19.6
通讯作者：
Crooker, Scott A.
中科院分区：
文献类型：
--
作者：
Yang, Luyi;Sinitsyn, Nikolai A.;Crooker, Scott A.
最近发现的单层过渡金属二硫属化物（TMDC）为探索新的耦合自旋谷物理提供了一个肥沃的操场（1-3）。尽管从偏振光致发光（PL）实验（4-8）推断出稳健的自旋和谷自由度，但是PL时间尺度必然受到短寿命（3-100 ps）电子-空穴复合的限制（9，10）。在电子（或空穴）掺杂的TMDC中的驻留载流子的自旋/谷极化动力学的直接探测（其可以在复合停止之后持续很长时间）处于早期阶段（11-13）。在这里，我们直接测量的耦合自旋谷动力学在电子掺杂的二硫化钼和WS 2单层使用光学克尔光谱，并揭示了非常长的电子自旋寿命，超过3纳秒在5 K（两到三个数量级长于典型的激子复合时间）。与传统的III-V族或II-VI族半导体相比，自旋弛豫在小的横向磁场中迅速加速。在耦合自旋-谷动力学模型的支持下，这些结果表明，在快速谷间散射驱动下，TMDCs中快速波动的内部自旋-轨道场中巡游电子自旋退相的新机制。此外，在较低的能量下观察到长寿命的自旋相干性，与局域态相称。这些研究提供了深入的物理基础自旋和谷动力学的原子薄TMDC中的居民电子。
The recently discovered monolayer transition metal dichalcogenides (TMDCs) provide a fertile playground to explore new coupled spin-valley physics(1-3). Although robust spin and valley degrees of freedom are inferred from polarized photoluminescence (PL) experiments(4-8), PL timescales are necessarily constrained by short-lived (3-100 ps) electron-hole recombination(9,10). Direct probes of spin/valley polarization dynamics of resident carriers in electron (or hole)-doped TMDCs, which may persist long after recombination ceases, are at an early stage(11-13). Here we directly measure the coupled spin-valley dynamics in electron-doped MoS2 and WS2 monolayers using optical Kerr spectroscopy, and reveal very long electron spin lifetimes, exceeding 3 ns at 5 K (two to three orders of magnitude longer than typical exciton recombination times). In contrast with conventional III-V or II-VI semiconductors, spin relaxation accelerates rapidly in small transverse magnetic fields. Supported by a model of coupled spin-valley dynamics, these results indicate a novel mechanism of itinerant electron spin dephasing in the rapidly fluctuating internal spin-orbit field in TMDCs, driven by fast inter-valley scattering. Additionally, a long-lived spin coherence is observed at lower energies, commensurate with localized states. These studies provide insight into the physics underpinning spin and valley dynamics of resident electrons in atomically thin TMDCs.