In spintronic THz emitters, the initial spin current leads to a local charge accumulation with a subsequent backflow. Although this effect strongly modifies the current profile, it is often not taken into account when the emitted THz radiation is used to extract the spin current physics. We demonstrate that the effect can be modeled using a simple equivalent circuit. It is, however, difficult to disentangle the backflow from the initial current. Besides the theory, we demonstrate that sub-wavelength THz emitters can be used to demonstrate the validity of the model by modifying the emission spectrum in a well-controlled way.
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