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Loss of interface spin transparency from conductivity mismatch in topological insulator based spintronic terahertz emitters

Jon K. Gustafson1,2, Nicholas S. Sirica1,*, Nicholas G. Combs1, Enrique D. Cobas1, Mehmet A. Noyan1, Connie H. Li1, and Olaf M. J. van ‘t Erve1,†

  • *Contact author: nicholas.s.sirica.civ@us.navy.mil
  • †Contact author: olaf.m.vanterve.civ@us.navy.mil
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Phys. Rev. B 113, 014302 – Published 6 January, 2026

DOI: https://doi.org/10.1103/3f1t-237k

Abstract

Terahertz emissions from magnetic heterostructures comprising Fermi-level engineered 3D topological insulators, Bi2Se3, are compared to assess how tuning the chemical potential absent any compositional change affects the resultant emission properties. Despite an enhancement in spin-orbit torque efficiency exhibited by bulk-insulating Bi2Se3 heterostructures, an ∼5-fold reduction in the terahertz emission amplitude is observed as compared to its bulk-conducting counterpart. Such discrepancy between reciprocal measurements of spin-charge conversion is understood to result from a loss of interface transparency to spin currents due to the low carrier density and high sheet resistance of bulk-insulating Bi2Se3, resulting in a pronounced conductivity mismatch between the metallic ferromagnet and topological insulating thin films that constitute our spintronic terahertz emitters.

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Phys. Rev. B 113, 014302– Published 6 January, 2026
  • Received 11 June 2025
  • Revised 15 October 2025
  • Accepted 3 December 2025
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