Ultrafast spin-charge conversion at SnBi$_2$Te$_4$/Co topological insulator interfaces probed by terahertz emission spectroscopy

TL;DR

This study demonstrates efficient spin-charge conversion at SnBi$_2$Te$_4$/Co topological insulator interfaces, using terahertz emission spectroscopy to probe the contribution of topological surface states to THz emission.

Contribution

It introduces a novel TI/ferromagnet interface design that avoids bulk band crossing, enabling clearer investigation of TSS-related spin-charge conversion via THz emission spectroscopy.

Findings

Significant THz emission observed from SnBi$_2$Te$_4$/Co junctions.

THz emission depends on TI thickness and angle, indicating TSS involvement.

THz emission TDS complements ARPES for interfacial spintronic studies.

Abstract

Spin-to-charge conversion (SCC) involving topological surface states (TSS) is one of the most promising routes for highly efficient spintronic devices for terahertz (THz) emission. Here, the THz generation generally occurs mainly via SCC consisting in efficient dynamical spin injection into spin-locked TSS. In this work, we demonstrate sizable THz emission from a nanometric thick topological insultator (TI)/ferromagnetic junction - SnBi$_2$Te$_4$/Co - specifically designed to avoid bulk band crossing with the TSS at the Fermi level, unlike its parent material Bi$_2$Te$_3$. THz emission time domain spectroscopy (TDS) is used to indicate the TSS contribution to the SCC by investigating the TI thickness and angular dependence of the THz emission. This work illustrates THz emission TDS as a powerful tool alongside angular resolved photoemission spectroscopy (ARPES) methods to investigate the interfacial spintronic properties of TI/ferromagnet bilayers.