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Abstract：
Thin-film stacks F|H consisting of a ferromagnetic-metal layer F and a heavy-metal layer H are spintronic model systems. Here, we present a method to measure the ultrabroadband spin conductance across a layer X between F and H at terahertz frequencies, which are the natural frequencies of spin-transport dynamics. We apply our approach to MgO tunneling barriers with thickness d = 0-6 Å. In the time domain, the spin conductance Gs has two components. An instantaneous feature arises from processes like coherent spin tunneling. Remarkably, a longer-lived component is a hallmark of incoherent resonant spin tunneling mediated by MgO defect states, because its relaxation time grows monotonically with d to as much as 270 fs at d = 6.0 Å. Our results are in full agreement with an analytical model. They indicate that terahertz spin-conductance spectroscopy will yield new and relevant insights into ultrafast spin transport in a wide range of spintronic nanostructures.
摘要：
由铁磁金属层F和重金属层H组成的薄膜堆叠F|H是自旋电子模型系统。这里,我们提出了一种在太赫兹频率下测量F和H之间的层X上的超宽带自旋电导的方法，这是自旋输运动力学的固有频率。我们将我们的方法应用于厚度d=0-6的MgO隧穿势垒。在时域中,自旋电导Gs具有两个分量。瞬时特征来自诸如相干自旋隧穿的过程。值得注意的是,寿命更长的成分是MgO缺陷态介导的非相干共振自旋隧道的标志，因为它的弛豫时间随d单调增长，在d=6.0µ时达到270fs。我们的结果与分析模型完全一致。他们表明，太赫兹自旋电导光谱将为各种自旋纳米结构中的超快自旋传输提供新的相关见解。
