Work

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

Year: 2025

Type: article

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 an F /TI model stack of a ferromagnetic-metal layer F ( Co and Fe ) and a topological-insulator (TI) layer ( Bi 2 Te 3 , Sn Bi 2 Te 4 , and Bi 1 − x Sb x with = 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 F in F and, thus, drive an ultrafast spin current out of F . SCI results in a transverse charge current with a sheet density I c that is detected by sampling of the emitted terahertz electric field. Analysis of the dynamics of I c () vs time relative to μ s F ( t ) reveals two components with distinct timescales: (1) a quasi-instantaneous response and (2) a longer-lived response with a relaxation time of 270 fs, which is independent of the F material chosen. Component (1) is consistently ascribed to the ISHE. In contrast, we interpret component (2) as a signature of interfacial spin accumulation and the IEE at the F / Bi 2 Te 3 interface, with a fraction of less than 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 allow us to differentiate the ISHE and the IEE and, more generally, provide important insights into the mechanisms of spin transport and SCI in F /TI stacks.

Source: Physical Review Applied

DOI: 10.1103/n1nw-2wyg