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THz-Radiation Generated from Interfacial Spin-Orbit Coupling

May 18, 2018 - Electromagnetic terahertz (THz) radiation is a versatile tool for a wide variety of sensing technologies ranging from security systems to medical applications.  Commonly, THz radiation is created using photoconductive switches and nonlinear crystals.  Recently, it was shown that optical excitation of fast spin current pulses in magnetic materials may generate strong THz radiation from transverse spin transport phenomena.  These experiments rely on a bulk conversion of spin currents into charge currents, which then subsequently generates THz radiation.

Now, writing in Physical Review Letters, Dr. Benjamin Jungfleisch and collaborators from Argonne National Laboratory have studied whether interfacial spin-orbit coupling phenomena may also be an efficient source for generating THz radiation.  For this purpose, a bilayer of Ag and Bi, which is known to exhibit strong Rashba-type spin-orbit coupling at its interface was combined with a ferromagnetic CoFeB layer. Upon optical excitation with a femtosecond laser pulse, Dr. Jungfleisch and collaborators observe the emission of THz radiation. Additional experiments with individual Ag and Bi layers show that this radiation originates from interfacial spin galvanic effects.  Furthermore, they demonstrate that the amplitude of the THz radiation depends on the helicity of the incident optical light pulse. These observations open up new perspectives for the development of ultrafast spintronic applications and devices where picosecond current pulses can be manipulated wirelessly by the helicity of light.

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M. B. Jungfleisch, Q. Zhang, W. Zhang, J. E. Pearson, R. D. Schaller, H. Wen, and A. Hoffmann,Phys. Rev. Lett. 120, 207207 (2018).