Ultrafast magnetization dynamics in perovskite films and heterostructures

在我们的提案中，我们想要研究强相关钙钛矿薄膜和异质结构中的光诱导超快自旋动力学，以及它们的电荷和晶格自由度的集体响应。我们特别感兴趣的是如何使用超快激光光掺杂来抑制和增强这些材料中的铁磁秩序，以及飞秒自旋电流如何作用于不同相的平衡。为了进行这类实验，通常采用飞秒时间分辨磁光克尔效应。然而，正如多年来所看到的那样，在测量的克尔信号中，通常不可能将相关材料的光致磁响应与电子和晶格响应分开。原因是自旋、电子和晶格对光激发的集体响应迅速改变了材料的折射率，这本身就改变了测量的瞬态克尔信号，因此无法提取纯磁响应。为了克服这一问题，并将超快自旋动力学的研究扩展到相关电子材料，我们将采用新的实验方法结合钙钛矿氧化物“对比”膜样品的研究。首先，我们将在光谱的极紫外区域使用我们最近开发的超快和元素特异性磁光Kerr技术，该技术对折射率的变化仅轻微敏感，因此是相关材料中“纯”磁化动力学的理想探针。此外，我们对光谱可见范围内瞬态克尔信号的理解的最新进展有助于我们解开自旋动力学、电子动力学和晶格动力学。此外，利用金属有机气溶胶沉积技术，我们将探索制备多种具有不同成分和调谐电子-自旋-晶格相关性的钙钛矿氧化物薄膜的独特可能性。以这种方式产生的“对比”样品将被检查其超快自旋动力学，帮助我们阐明，例如，电子-声子耦合在最佳掺杂锰矿石（去）磁化动力学中的作用。在未来，对相关材料的光诱导自旋动力学的深入研究可能会开辟一条可能的研究方向，从对非平衡相关物理的更深入理解扩展到通过光激发产生瞬态“隐藏”态。

In our proposal, we want to investigate photo-induced ultrafast spin dynamics in strongly-correlated perovskite thin films and heterostructures, together with their collective response of charge and lattice degrees of freedom. In particular, we are interested how photo-doping with ultrafast lasers can be used to suppress and enhance ferromagnetic order in these materials, and how femtosecond spin-currents act on the balance of different phases. In order to carry out such experiments, the femtosecond time-resolved magneto-optical Kerr effect is usually applied. However, as has been seen for many years, it is very often impossible to disentangle the photo-induced magnetic response of correlated materials from the electronic and lattice response in the measured Kerr signals. The reason is that the collective response of spins, electrons and lattice to a photo-excitation rapidly changes the refractive index of the material, which itself modifies the measured transient Kerr signal, so that the pure magnetic response cannot be extracted.In order to overcome this problem, and to extend the investigation of ultrafast spin dynamics towards correlated electron materials, we will apply new experimental methods in combination with studies on “contrast” film samples of perovskite oxides. First, we will use our recently developed ultrafast and element-specific magneto-optical Kerr technique in the extreme ultraviolet region of the spectrum, which is only marginally sensitive to changes of the refractive index, and, therefore, is an ideal probe of “pure” magnetization dynamics in correlated materials. In addition, recent progress in our understanding of transient Kerr signals in the visible range of the spectrum helps us to disentangle spin-, electron-, and lattice dynamics. Furthermore, using the metalorganic aerosol deposition technique, we will explore the unique possibility to prepare a multitude of thin perovskite oxide films with different composition and tuned electron-spin-lattice correlations. The in this way produced “contrast” samples will be examined with respect to their ultrafast spin dynamics, helping us to elucidate, for instance, the role of electron-phonon coupling on the (de)magnetization dynamics in optimally doped manganites. In the future, a distinct access to the photo-induced spin dynamics in correlated materials might open up an avenue of possible research directions, spreading from a deeper understanding of the non-equilibrium correlation physics towards generation of transient “hidden” states via photo-excitation.