Terahertz time-domain signatures of the inverse Edelstein effect in topological-insulator|ferromagnet heterostructures

Abstract

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 ${\mu }_s^{\mathcal{F}}$ 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 ${\mu }_s^{\mathcal{F}}(t)$ 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.

References in corpus (14)

• Emergent quantum confinement at topological insulator surfaces
• Ultrafast surface carrier dynamics in the topological insulator Bi2Te3
• Surface state dominated spin-charge current conversion in topological insulator/ferromagnetic insulator heterostructures
• Spintronic Sources of Ultrashort Terahertz Electromagnetic Pulses
• Control of spin-orbit torques by interface engineering in topological insulator heterostructures
• Dirac-Surface-State-Dominated Spin to Charge Current Conversion in the Topological Insulator $(B{i}_{0.22}S{b}_{0.78}{)}_{2}T{e}_3$ Films at Room Temperature
• Ultrafast photothermoelectric effect in Dirac semimetallic Cd3As2 revealed by terahertz emission
• Ultrafast Energy- and Momentum-resolved Surface Dirac Photocurrents in the Topological Insulator Sb${}_2$Te${}_3$
• Frequency-independent terahertz anomalous Hall effect in DyCo${}_5$, Co${}_{32}$Fe${}_{68}$ and Gd${}_{27}$Fe${}_{73}$ thin films from DC to 40 THz
• Ultrafast spin-charge conversion at SnBi${}_2$Te${}_4$/Co topological insulator interfaces probed by terahertz emission spectroscopy
• Light and microwave driven spin pumping across FeGaB-BiSb interface
• Thermal Conductivity of Oxide Tunnel Barriers in Magnetic Tunnel Junctions Measured by Ultrafast Thermoreflectance and Magneto-optic Kerr Effect Thermometry
• Exploiting the close-to-Dirac point shift of Fermi level in Sb2Te3/Bi2Te3 topological insulator heterostructure for spin-charge conversion
• Thickness-dependent electron momentum relaxation times in iron films

Cited by in corpus (1)

• Spin and Orbital Rashba response in ferroelectric polarized PtSe${}_2$/MoSe${}_2$/LiNbO${}_3$ heterostructures