标题： 在LaAlO$_{3}$的太赫兹克尔效应响应中解析电子和离子非线性极化效应 显示英文标题

标题： Disentangling Electronic and Ionic Nonlinear Polarization Effects in the THz Kerr Response of LaAlO$_{3}$

摘要： 强太赫兹（THz）场的非线性响应为当代材料系统的复杂动力学提供了独特的见解。 然而，在太赫兹克尔效应中区分真实的离子振荡和瞬时电子响应仍然具有挑战性。 在这里，我们结合二维太赫兹克尔效应（2D-TKE）光谱实验及其建模，揭示了在低温下孪晶LaAlO$_3$晶体中太赫兹诱导的时间振荡的复杂性。 我们将1.1 THz模式识别为$E_g$拉曼声子，而0.86 THz和0.36 THz信号是由于双折射孪晶域中太赫兹和光学探测脉冲的同向和反向传播引起的虚假效应。 此外，我们确定$E_g$模式是通过双光子过程激发的，而样品表面的太赫兹脉冲反射会产生可以模拟非谐声子耦合的时域响应。 我们的研究强调了非线性太赫兹实验中传播效应的重要性，并为解释双折射晶体中的太赫兹偏振动力学提供了更精炼的框架。 显示英文摘要

摘要： Nonlinear responses to intense terahertz (THz) fields provide unique insights into complex dynamics of contemporary material systems. However, the interpretation of the obtained data, in particular, distinguishing genuine ionic oscillations from the instantaneous electronic responses in THz Kerr effect remains challenging. Here, we combine two-dimensional Terahertz Kerr effect (2D-TKE) spectroscopy experiments and their modeling to unravel complex THz-induced temporal oscillations in twinned LaAlO$_3$ crystals at low temperatures. We identify the 1.1 THz mode as $E_g$ Raman phonon, while 0.86 THz and 0.36 THz signals are due to spurious effects resulting from the co- and counter-propagation of THz and optical probe pulses in birefringent twin domains. Furthermore, we determine that the $E_g$ mode is excited via a two-photon process, whereas THz pulse reflections at the sample surface produce a temporal response that can mimic anharmonic phonon coupling. Our findings highlight the importance of propagation effects in nonlinear THz experiments and provide a refined framework for interpreting THz polarization dynamics in birefringent crystals.