SKM 2021 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 6: Focus Session: Magnon Polarons - Magnon-Phonon Coupling and Spin Transport (joint session MA/HL)

HL 6.5: Hauptvortrag

Montag, 27. September 2021, 15:15–15:45, H5

Magnon polarons and the low-temperature spin-Seebeck effect — •Piet Brouwer and Rico Schmidt — Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany

Using a simplified microscopic model of coupled spin and lattice excitations in a ferromagnetic insulator we evaluate the magnetic-field dependence of the longitudinal spin Seebeck effect at low temperatures. We find that at low temperatures, large magnetic fields, and for not-too-large system sizes the spin Seebeck effect is almost completely mediated by magnon polarons, superpositions of magnon and phonon excitations, with frequency close to the crossing points of magnon and phonon dispersions. We find an enhancement of the spin-Seebeck effect for ``critical'' values of the magnetic field, for which magnon and phonon dispersions touch. Such an enhancement of the longitudinal spin-Seebeck effect was observed experimentally by Kikkawa et al. [Phys. Rev. Lett. 117, 207203 (2016)]. We find that the existence of this enhancement is independent of the relative strength of magnon-impurity and phonon-impurity scattering.