Dominance of the first excitation step for magnetic circular dichroism in near-threshold two-photon photoemission
Dominance of the first excitation step for magnetic circular dichroism in near-threshold two-photon photoemission
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近阈值双光子光电发射中磁圆二色性第一激发步骤的主导地位
DOI：
10.1103/physrevb.85.014426
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发表时间：
2012
影响因子：
3.7
通讯作者：
P.M. Oppeneer
中科院分区：
文献类型：
--
作者：
K. Hild;G. Schönhense;H. J. Elmers;T. Nakagawa;T. Yokoyama;K. Tarafder;P.M. Oppeneer
测量了垂直磁化的Cs/Co/Pt（111）薄膜的近阈值光电子发射磁圆二色性（MCD），其功函数由Cs吸附调节。对于单光子光电发射（1 PPE）的MCD不对称性记录在一个固定的光子能量h= 3.06 eV和不同的功函数。非对称性随过剩能h-的变化表现出非单调性，在2.45eV处有最大值A = 6.2。该测量探索了前一个双光子光电发射（2 PPE）测量的第一激发步骤，其中A = 8.4，表明在来自Co（111）的2 PPE中，第一激发步骤是主要的不对称产生过程。在约化功函数（3 eV）下的2 PPE中的能量依赖测量在h= 1.53-1.66 eV之间的光子能量范围内产生约17的恒定不对称性。结果表明，对于Co（111），一个真实的中间态的参与是增大MCD不对称性的关键.这两个结果进行了讨论的框架内的直接带间跃迁的方向偏离正常的电子发射方向-L。1 PPE测量与基于该模型的计算结果合理一致。这表明，anab initicalculation考虑所有方向的激发与额外的限制，由于在光电子过程中的样品功函数的存在，能量充分描述MCD不对称性在近阈值光电子。
Magnetic circular dichroism (MCD) in near-threshold photoemission is measured for a perpendicularly magnetized Cs/Co/Pt(111) film with work function adjusted by Cs adsorption. For one-photon photoemission (1PPE) the MCD asymmetry is recorded at a fixed photon energy of h= 3.06 eV and varying work function. The asymmetry shows a nonmonotonous behavior in dependence of the excess energy h-with a maximum value ofA= 6.2at= 2.45 eV. The measurement explores the first excitation step of a former two-photon photoemission (2PPE) measurement withA= 8.4demonstrating that in 2PPE from Co(111) the first excitation step is the dominant asymmetry-generating process. An energy-dependent measurement in 2PPE at reduced work function (3 eV) yields a constant asymmetry of about 17in the photon energy range between h= 1.53–1.66 eV. It reveals that for Co(111) the involvement of a real intermediate state is crucial for enlarged MCD asymmetries. Both results are discussed in the framework of direct interband transitions in directions deviating from the direction of normal electron emission-L. The 1PPE measurement is in reasonable agreement with calculations on the basis of this model. This reveals that anab initiocalculation considering all directions of excitation with an additional restriction in energy due to the existence of the sample work function in the photoemission process adequately describes MCD asymmetries in near-threshold photoemission.