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MA: Fachverband Magnetismus

MA 24: Terahertz Spintronics I

MA 24.6: Vortrag

Mittwoch, 20. März 2024, 10:45–11:00, EB 202

Terahertz spin transport and spin charge conversion dynamics in topological-insulator|ferromagnet heterostructures — •Genaro Bierhance^1,2, Chihun In², Enzo Rongione^3,4, Reza Rouzegar², Oliver Gueckstock², Emanuele Longo^5,6, Tom Sebastian Seifert², Roberto Mantovan⁵, Henri Jaffrès³, Athanasios Dimoulas⁷, and Tobias Kampfrath^1,2 — ¹FHI Berlin, Germany — ²FU Berlin, Germany — ³CNRS, Paris, France — ⁴ICN2, Barcelona, Spain — ⁵CNR-IMM, Italy — ⁶ICMAB, Barcelona, Spain — ⁷NCSRD, Athens, Greece

Topological insulators are promising materials for terahertz (THz) spintronic devices due to their topologically protected surface states with spin-momentum locking, which unveil channels for spin-charge interconversion (SCI). Here, we study ultrafast spin transport and SCI in F|TI stacks consisting of a ferromagnetic metal layer (F) and a topological-insulator film (TI). An incident femtosecond laser pulse induces a spin voltage and, thus, spin transport from F to TI. Subsequent SCI launches a transverse charge current that emits a broadband THz electromagnetic pulse. A detailed analysis of the obtained THz emission signal dynamics in the TI Bi₂Te₃ reveals two relaxation components with distinct time scales: a quasi-instantaneous and a significantly longer response. Remarkably, the extracted time constant (300 fs) of the latter is independent of the chosen F material (Fe or Co). We ascribe these observations to a slower response of either spin transport or SCI in Bi₂Te₃, indicating the importance of intermediate states in these structures.

Keywords: terahertz; spintronics; topological insulators; ultrafast spin transport; spin charge current interconversion