Terahertz time-domain signatures of the inverse Edelstein effect in topological-insulator|ferromagnet heterostructures
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2025
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| author | Bierhance, Genaro In, Chihun Rongione, Enzo Rouzegar, Reza Gueckstock, Oliver Longo, Emanuele Baringthon, Laëtitia Reyren, Nicolas Lebrun, Romain George, Jean-Marie Tsipas, Polychronis Wolf, Martin Seifert, Tom S. Mantovan, Roberto Jaffrès, Henri Dimoulas, Athanasios Kampfrath, Tobias |
| author_facet | Bierhance, Genaro In, Chihun Rongione, Enzo Rouzegar, Reza Gueckstock, Oliver Longo, Emanuele Baringthon, Laëtitia Reyren, Nicolas Lebrun, Romain George, Jean-Marie Tsipas, Polychronis Wolf, Martin Seifert, Tom S. Mantovan, Roberto Jaffrès, Henri Dimoulas, Athanasios Kampfrath, Tobias |
| contents | Three-dimensional topological insulators possess topologically protected surface states with spin-momentum locking, which enable spin-charge-current interconversion (SCI) by the inverse Edelstein effect (IEE). However, it remains experimentally challenging to separate the surface-related IEE from the bulk-type inverse spin Hall effect (ISHE). Here, we search for distinct time-domain signatures of the two SCI phenomena in a $\mathcal{F}$|TI model stack of a ferromagnetic-metal layer $\mathcal{F}$ (Co and Fe) and a topological-insulator layer TI (Bi$_2$Te$_3$, SnBi$_2$Te$_4$ and Bi$_{1-x}$Sb$_x$ with $x$ = 0.15 and 0.3), where the focus is on Bi$_2$Te$_3$. A femtosecond laser pulse serves to induce a transient spin voltage $μ_s^{\mathcal{F}}$ in $\mathcal{F}$ and, thus, drive an ultrafast spin current out of $\mathcal{F}$. SCI results in a transverse charge current with a sheet density $I_c$ that is detected by sampling the emitted terahertz electric field. Analysis of the dynamics of $I_c(t)$ vs time $t$ relative to $μ_s^{\mathcal{F}}(t)$ reveals two components with distinct time scales: (i) a quasi-instantaneous response and (ii) a longer-lived response with a relaxation time of 270 fs, which is independent of the chosen $\mathcal{F}$ material. Component (i) is consistently ascribed to the ISHE. In contrast, we interpret component (ii) as a signature of interfacial spin accumulation and the IEE at the $\mathcal{F}$/Bi$_2$Te$_3$ interface, with a fraction of $< 10^{-2}$ of the incident spins participating. This assignment is fully consistent with respect to its dynamics and magnitude. We rate other possible signal contributions, such as spin trapping in intermediate states, as less likely. Our results show that the femtosecond dynamics of photocurrents provide important insights into the mechanisms of spin transport and SCI in $\mathcal{F}$|TI stacks. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2506_22327 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Terahertz time-domain signatures of the inverse Edelstein effect in topological-insulator|ferromagnet heterostructures Bierhance, Genaro In, Chihun Rongione, Enzo Rouzegar, Reza Gueckstock, Oliver Longo, Emanuele Baringthon, Laëtitia Reyren, Nicolas Lebrun, Romain George, Jean-Marie Tsipas, Polychronis Wolf, Martin Seifert, Tom S. Mantovan, Roberto Jaffrès, Henri Dimoulas, Athanasios Kampfrath, Tobias Mesoscale and Nanoscale Physics Three-dimensional topological insulators possess topologically protected surface states with spin-momentum locking, which enable spin-charge-current interconversion (SCI) by the inverse Edelstein effect (IEE). However, it remains experimentally challenging to separate the surface-related IEE from the bulk-type inverse spin Hall effect (ISHE). Here, we search for distinct time-domain signatures of the two SCI phenomena in a $\mathcal{F}$|TI model stack of a ferromagnetic-metal layer $\mathcal{F}$ (Co and Fe) and a topological-insulator layer TI (Bi$_2$Te$_3$, SnBi$_2$Te$_4$ and Bi$_{1-x}$Sb$_x$ with $x$ = 0.15 and 0.3), where the focus is on Bi$_2$Te$_3$. A femtosecond laser pulse serves to induce a transient spin voltage $μ_s^{\mathcal{F}}$ in $\mathcal{F}$ and, thus, drive an ultrafast spin current out of $\mathcal{F}$. SCI results in a transverse charge current with a sheet density $I_c$ that is detected by sampling the emitted terahertz electric field. Analysis of the dynamics of $I_c(t)$ vs time $t$ relative to $μ_s^{\mathcal{F}}(t)$ reveals two components with distinct time scales: (i) a quasi-instantaneous response and (ii) a longer-lived response with a relaxation time of 270 fs, which is independent of the chosen $\mathcal{F}$ material. Component (i) is consistently ascribed to the ISHE. In contrast, we interpret component (ii) as a signature of interfacial spin accumulation and the IEE at the $\mathcal{F}$/Bi$_2$Te$_3$ interface, with a fraction of $< 10^{-2}$ of the incident spins participating. This assignment is fully consistent with respect to its dynamics and magnitude. We rate other possible signal contributions, such as spin trapping in intermediate states, as less likely. Our results show that the femtosecond dynamics of photocurrents provide important insights into the mechanisms of spin transport and SCI in $\mathcal{F}$|TI stacks. |
| title | Terahertz time-domain signatures of the inverse Edelstein effect in topological-insulator|ferromagnet heterostructures |
| topic | Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2506.22327 |