Spin-polarized image-potential-state electrons as ultrafast magnetic sensors in front of ferromagnetic surfaces Englisch:

在双光子光电发射中，对线宽和寿命的联合测量，或者在相干激发多个态后量子拍子的衰减，提供了对准弹性和非弹性电子散射过程的洞察。在铁磁表面上，这些散射过程包括斯通纳激发和电子-磁振子激发，因此是基本理解超快磁化过程的关键因素。像态电子是一个定义明确的模型系统，它的表面前面的距离，即探测表面积，和寿命可以通过选择量子数来改变一个数量级。在铁磁表面，这些态是自旋分裂的，寿命展宽与自旋有关。因此，这些态反映了交换分裂的体带隙边界，并允许直接从ps到ps的时间尺度来研究与自旋相关的驰豫过程。将有序的巡游铁磁性薄膜作为简单的模型系统进行了研究。不同厚度的薄膜可以改变居里温度和表面磁化强度。我们将讨论这些参数对自旋相关的非弹性和弹性散射的影响。居里点以下和以上的测量用来区分铁磁和顺磁状态的固有性质。这为研究飞秒激光脉冲驱动的超快退磁过程提供了前景。本项目二期计划进行相应的实验。

The combined measurement of linewidth and lifetime or the decay of quantum beats after coherent excitation of several states in two-photon photoemission delivers insight to quasielastic and inelastic electron scattering processes. On ferromagnetic surfaces these scattering processes include Stoner and electron-magnon excitations and are thus key ingredients for a fundamental understanding of ultrafast magnetization processes. Image-state electrons serve as a well-defined model system for which the distance in front of the surface, i.e. the probed surface area, and the lifetime can be varied about an order of magnitude by choice of the quantum number. On ferromagnetic surfaces these states are spin split and the lifetime broadening is spin dependent. The states thus reflect the exchange-split bulk-band gap boundaries and allow to study spin-dependent relaxation processes directly from the fs to ps time scale. Well-ordered itinerant ferromagnetic films are examined as simple model systems. Films of different thicknesses allow to vary the Curie temperature and surface magnetization. The influence of these parameters on spin-dependent inelastic and elastic scattering will be addressed. Measurements below and above the Curie point are used to distinguish between inherent properties of the ferromagnetic and paramagnetic states. This gives the perspective to study ultrafast demagnetization processes driven by femtosecond laser pulses. Corresponding experiments are planned in the second period of this project.