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

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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.