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

在双光子光电子发射中，几个态的相干激发后，线宽和寿命或量子拍频衰减的联合测量提供了准弹性和非弹性电子散射过程的见解。在铁磁表面上，这些散射过程包括斯通纳和电子磁振子激发，因此是对超快磁化过程的基本理解的关键成分。镜像态电子作为一个定义明确的模型系统，其表面前的距离，即探测的表面积，和寿命可以通过选择量子数而变化大约一个数量级。在铁磁表面上，这些状态是自旋分裂的，并且寿命展宽是自旋相关的。因此，国家反映了交换分裂体带隙边界，并允许研究自旋相关的弛豫过程直接从fs到ps的时间尺度。有序巡游铁磁薄膜作为简单的模型系统进行检查。不同厚度的膜允许改变居里温度和表面磁化。这些参数对自旋相关的非弹性和弹性散射的影响将得到解决。居里点以下和以上的测量用于区分铁磁和顺磁状态的固有特性。这为研究飞秒激光脉冲驱动的超快退磁过程提供了前景。计划在该项目的第二阶段进行相应的实验。

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.