Theoretical calculations of high-harmonic generation (HHG) from commensurate twisted bilayer graphene (tBLG) under intense laser fields are performed. The nonlinear electron dynamics in tBLG is considered by solving the Liouville–von Neumann equation for a single-particle density matrix, which combines the full energy bands and momentum matrix elements within the framework of tight-binding approximation. We show that the pump intensity determines the relative magnitude of two components of the harmonic spectrum parallel and perpendicular to driving polarization. The important dependence of HHG on twisted angles and crystal orientations is also presented. Especially in the absence of the relaxation process, the harmonic emission for twisted angles around 10 ° exhibits an evident decrease in efficiency per layer compared to monolayer graphene (MLG), which can be interpreted according to Fermi velocity modification. Our calculation also shows that the relative emission efficiency of different harmonic orders between tBLG and MLG contains redundant information on both the dephasing time and an empirical parameter characterizing the decay of the interlayer electron hopping, thus suggesting an all-optical method for the reconstruction of the two parameters. The reconstruction feasibility is successfully demonstrated by a simple optimization algorithm even if considering the possible experimental uncertainty of both driving pulse parameters and high-harmonic signals. Our results show that HHG spectroscopic characteristics in tBLG might serve as a fingerprint to identify the geometric stacking angle and the electronic interaction between adjacent layers, as well as the strong-field laser induced ultrafast dephasing process.

中文翻译：

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由中红外激光场驱动的扭曲双层石墨烯产生高次谐波

在强激光场下，对来自相称扭曲双层石墨烯 (tBLG) 的高次谐波产生 (HHG) 进行了理论计算。tBLG 中的非线性电子动力学通过求解单粒子密度矩阵的 Liouville-von Neumann 方程来考虑，该方程在紧束缚近似的框架内结合了全能带和动量矩阵元素。我们表明泵浦强度决定了平行和垂直于驱动偏振的谐波频谱的两个分量的相对大小。还介绍了 HHG 对扭曲角和晶体取向的重要依赖性。特别是在没有弛豫过程的情况下，与单层石墨烯 (MLG) 相比，10° 左右扭曲角的谐波发射表现出每层效率的明显下降，这可以根据费米速度修正来解释。我们的计算还表明，tBLG 和 MLG 之间不同谐波阶次的相对发射效率包含关于移相时间和表征层间电子跳跃衰减的经验参数的冗余信息，因此提出了一种全光学方法来重建两个参数。即使考虑到驱动脉冲参数和高谐波信号的可能实验不确定性，重建的可行性也通过简单的优化算法成功证明。我们的结果表明 tBLG 中的 HHG 光谱特征可以作为指纹来识别几何堆叠角和相邻层之间的电子相互作用，