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Terahertz Magneto-Photocurrents in the Topological Insulator Bi2Se3 Probe Its Topological Surface States

Chihun In1,2,*, Genaro Bierhance1,2, Deepti Jain3, Tom S. Seifert1, Oliver Gueckstock1, Roberto Mantovan4, Seongshik Oh3,5, and Tobias Kampfrath1,2

  • *Contact author: chihun.in@fu-berlin.de
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Phys. Rev. Lett. 137, 106601 – Published 2 September, 2026

DOI: https://doi.org/10.1103/yvbq-rdkz

Abstract

We study ultrafast magneto-photocurrents in a three-dimensional topological insulator. For this purpose, we excite (InrBi1−r)2Se3 thin films with a femtosecond laser pulse in the presence of an external magnetic field Bext up to 0.3  T parallel to the film plane. The resulting in-plane photocurrent is measured by detecting the emitted terahertz electromagnetic pulse. It is proportional and perpendicular to Bext. Strikingly, for r≥4%, we observe an abrupt photocurrent reduction, which is strongly correlated with the indium-induced quenching of the topological surface states. The rise time, decay time, and amplitude of the terahertz magneto-photocurrent can consistently be explained by the following scenario: optically excited spin-polarized electrons propagate toward the film surface where the accumulated spin is converted into an in-plane charge current due to spin-velocity locking. Our results are highly relevant for contact-free probing of spin-charge conversion in systems without spontaneous magnetic order and without having to add invasive spin-source layers.

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Outline

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Phys. Rev. Lett. 137, 106601– Published 2 September, 2026
  • Received 2 April 2024
  • Revised 21 July 2026
  • Accepted 24 July 2026
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