Spin-flip radiation sources based on magnetic point-contact arrays

拟议项目旨在实验演示磁性和非磁性材料之间纳米结中的一种新物理现象，即自旋翻转光电发射。这种效应已经被理论预测，但没有直接的实验证明。创造一种新型的自旋电子学是固态物理中最深入研究的课题之一。在自旋电子学的发展领域中，统一的特征是利用电子的自旋自由度而不是其电荷来实现特定的器件功能。最近的发展目标是在高度非平衡制度的磁性纳米系统的调查。在这种纳米尺度下，磁结的一些最重要的问题包括光和热与自旋极化和纯自旋电流的相互作用。在最近的理论报告中，A. Kadigrobov和R. Shekhter等人提出了一种新型的辐射源，其基础是在磁性金属点接触中产生自旋-布居数反转。其基本思想是将铁磁体中的自旋极化电流注入正常金属或稀铁磁体的能量分裂自旋子带中，以产生自旋粒子数反转。这种非平衡自旋-布居反转可以通过自旋翻转跃迁衰减，在某些情况下，这导致光子的发射，其频率由自旋子带的能量分裂决定。取决于活性材料，可访问的频率范围涵盖微波（GHz）和THz辐射。根据该理论，这些辐射源将是高度可调的，与尖端半导体器件相比具有巨大的强度。因此，这种器件在许多技术应用中具有巨大的潜力，例如通信电子、数据存储、光学传感和可编程逻辑器件。然而，目前的概念自旋翻转激光在磁点接触依赖于理论预测的效果。本计画将提供磁性异质接面自旋反转光电效应的直接实验示范。我们将制作和表征铁磁体与正常金属或稀铁磁体之间的点接触阵列。通过输运光谱测量的临界参数，自旋粒子数反转发生的评估。基于这些信息，从点接触阵列在GHz和太赫兹范围内的自旋翻转光电发射的刺激，可以用光学检测。然后将详细研究器件的光学增益和发射辐射的光谱特性。此外，本计画将进一步发展磁性异质接面自旋反转雷射的理论，并提供详细的元件模型。这些调查是重要的贡献，在纳米级，磁性异质结的自旋相关的，非平衡输运现象的理解。

The proposed project aims at the experimental demonstration of a novel physical phenomenon, namely spin-flip photo-emission, in nano-junctions between magnetic and non-magnetic materials. This effect has been predicted by theory but there is no direct experimental demonstration.The creation of a novel type of spin-electronics is one of the most intensively researched topics in solid-state physics. The unifying characteristic in the advancing field of spin-electronics is that the spin degree of freedom of the electron rather than its charge is exploited to achieve a specific device functionality. Recent developments aim at the investigation of magnetic nanoscale systems in highly non-equilibrium regimes. In such nanoscale, magnetic junctions some of the most important issues include the interaction of light and heat with spin-polarized and pure spin currents. In recent theoretical reports, A. Kadigrobov and R. Shekhter et al. proposed a novel type of radiation source, based on the creation of a spin-population inversion in magnetic, metallic point contacts. The basic idea is to inject a spin-polarized current from a ferromagnet in the energy-split spin-subbands of a normal metal or a dilute ferromagnet to create a spin-population inversion. This non-equilibrium spin-population inversion can decay via spin-flip transitions, which, under certain circumstances, results in the emission of photons, whose frequency is determined by the energy-splitting of the spin-subbands. Depending on the active material, the accessible frequency range covers both microwave (GHz) and THz radiation. According to the theory, these radiation sources would be highly tunable and of giant intensity compared to cutting-edge semiconductor devices. Hence, such devices would have enormous potential in numerous technical applications, e.g. communication electronics, data storage, optical sensing and programmable logic devices. However, presently the concept of spin-flip lasing in magnetic point contacts rests on theoretical predictions of the effect. The proposed project will provide a direct experimental demonstration of spin-flip photoemission in magnetic heterojunctions. We will fabricate and characterize point contact arrays between a ferromagnet and a normal metal or dilute ferromagnet. The critical parameters, where a spin-population inversion occurs are evaluated via transport spectroscopy measurements. Based on these information, spin-flip photoemission from point contact arrays in the GHz and THz range is stimulated and can be detected optically. The optical gain of the devices and spectral properties of the emitted radiation will then be studied in detail. Additionally, the proposed project will advance the theory of spin-flip lasing in magnetic heterojunctions and provide a detailed device model. These investigations are important contributions to the understanding of spin-dependent, non-equilibrium transport phenomena in nanoscopic, magnetic heterojunctions.