Abstract A theoretical investigation on the coherent Dirac-like quasiparticle dynamics in monolayer MoS 2 under an ultrashort optical pulse irradiation is presented. Particularly, we remain specific features of monolayer molybdenum disulfide (ML-MDS) associated with the mass asymmetry α and topological aspect β parameters resulting in Schrodinger type wavevector of charge carriers. The direct band gap, spin-resolved valence band splitting and valley degeneracy breaking due to strong spin–orbit coupling affect ultrafast dynamics of Dirac fermions. Because the duration of the optical pulse is less than the electron scattering time, which is ∼ 10 − 100 fs, the electron dynamics in electric field of the optical pulse is coherent, and consequently, we can describe the coupling of electron with strong electromagnetic field by the time-dependent Schrodinger equation. The conduction band and valence band coupling via the strong electric field of pulse ( 0 . 2 − 2 . 5 V/A) gives rise to appearance of a dipole moment during the pulse is applied. We find that the dipole is complex, originating from the existence of band gap. We show an asymmetric singularities in Dirac points for absolute of dipole moment. We solve the resulting coupled evolution equations for the expansion coefficient of valence and conduction bands to obtain probability of population transition between valence and conduction bands. The irreversible electron dynamics as a key feature of two-dimensional Dirac matters in interacting with an ultrashort pulse strongly depends on the electronic structure of MoS 2 . Furthermore, we present conduction band population distribution with an asymmetric exhibition at the each pair of Dirac points ( K and K ′ ), when the pulse ends. This leads to valley polarization effect. The forced electric current is transferred on the surface of ML-MDS in the pulse field direction, due to irreversible dynamics. These results can convince possibility to introduce device-friendly optoelectronic applications for MoS 2 .

中文翻译：

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超短光脉冲下单层二硫化钼的相干电子动力学

摘要 提出了在超短光脉冲照射下单层MoS 2 中相干狄拉克类准粒子动力学的理论研究。特别是，我们保留了与质量不对称 α 和拓扑方面 β 参数相关的单层二硫化钼 (ML-MDS) 的特定特征，导致电荷载体的薛定谔型波矢。由于强自旋-轨道耦合导致的直接带隙、自旋分辨价带分裂和谷简并断裂影响狄拉克费米子的超快动力学。由于光脉冲的持续时间小于电子散射时间，即 ∼ 10 - 100 fs，光脉冲电场中的电子动力学是相干的，因此，我们可以用时变薛定谔方程来描述电子与强电磁场的耦合。通过脉冲强电场（0 . 2 - 2 . 5 V/A）的导带和价带耦合在施加脉冲期间引起偶极矩的出现。我们发现偶极子是复杂的，源于带隙的存在。我们在 Dirac 点中展示了偶极矩绝对值的非对称奇点。我们求解由此产生的价带和导带膨胀系数的耦合演化方程，以获得价带和导带之间的种群转变概率。作为二维狄拉克物质与超短脉冲相互作用的关键特征的不可逆电子动力学强烈依赖于 MoS 2 的电子结构。此外，当脉冲结束时，我们在每对狄拉克点（ K 和 K ' ）处呈现具有不对称表现的导带种群分布。这导致谷极化效应。由于不可逆动力学，强制电流沿脉冲场方向在 ML-MDS 表面传输。这些结果可以说服为 MoS 2 引入设备友好的光电应用的可能性。