Coherent control of terahertz-scale spin resonances using optical spin-orbit torques

Using optically generated spin-orbit torques induced by the heavy metal Pt we demonstrate coherent control of GHz ferromagnetic resonances in Pt/Co/Pt multilayers as well as sub-THz exchange resonances in [Gd/Co]$_2$ multilayers. Employing a double-pump setup, we show that depending on the helicities of the pump pulses, spin resonances can either be coherently amplified or suppressed if the time delay between the arrival of the pump beams is chosen appropriately. Furthermore, investigating phase and amplitude of the exchange-driven modes, we identify features that challenge the current understanding of optically generated spin-orbit torques, and we discuss possible explanations.