Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy

• DOI: 10.1038/s41467-018-05135-2
• Publication Date: 2018-07-18T18:37:29Z
• Authors: Tom S. Seifert; Samridh Jaiswal; Joseph Barker; Sebastian T. Weber; Ilya Razdolski; Joel Cramer; Oliver Gueckstock; Sebastian F. Maeh...; Lukas Nadvornik; Shun Watanabe; Chiara Ciccarelli; Alexey Melnikov; Gerhard Jakob; Markus Münzenberg; Sebastian T. B. G...; Georg Woltersdorf; Baerbel Rethfeld; Piet W. Brouwer; Martin Wolf; Mathias Kläui; Tobias Kampfrath
• Keywords: Condensed Matter - Materials Science; Condensed Matter - Mesoscale and Nanoscale Physics; 530 Physics; Science; 0299 Other Physical Sciences; ddc:530; Q; Materials Science (cond-mat.mtrl-sci); FOS: Physical sciences; Spintronics; 530 Physik; 530; 7. Clean energy; Article; 537; Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Terahertz optics

AbstractUnderstanding the transfer of spin angular momentum is essential in modern magnetism research. A model case is the generation of magnons in magnetic insulators by heating an adjacent metal film. Here, we reveal the initial steps of this spin Seebeck effect with <27 fs time resolution using terahertz spectroscopy on bilayers of ferrimagnetic yttrium iron garnet and platinum. Upon exciting the metal with an infrared laser pulse, a spin Seebeck current js arises on the same ~100 fs time scale on which the metal electrons thermalize. This observation highlights that efficient spin transfer critically relies on carrier multiplication and is driven by conduction electrons scattering off the metal–insulator interface. Analytical modeling shows that the electrons’ dynamics are almost instantaneously imprinted onto js because their spins have a correlation time of only ~4 fs and deflect the ferrimagnetic moments without inertia. Applications in material characterization, interface probing, spin-noise spectroscopy and terahertz spin pumping emerge.