Theory of spin and orbital charge conversion at the surface states of Bi_{1-x}Sb_x topological insulator

TL;DR

This paper investigates the spin and orbital charge conversion mechanisms at the surface states of Bi_{1-x}Sb_x topological insulators, combining theoretical, numerical, and experimental approaches to enhance understanding of their potential in spintronic applications.

Contribution

It introduces a theoretical and numerical analysis of orbital momentum-locking and orbital Rashba-Edelstein effects in Bi_{0.85}Sb_{0.15}, expanding on previous experimental findings.

Findings

Quantification of orbital charge conversion effects.

Theoretical insights into orbital Rashba-Edelstein effects.

Numerical modeling using multi-orbital tight-binding methods.

Abstract

Topological insulators are quantum materials involving Time-reversal protected surface states(TSS) making them appealing candidates for the design of next generation of highly efficient spintronic devices. The very recent observation of large transient spin-charge conversion (SCC) and subsequent powerful THz emission from Co|Bi_{1-x}Sb_x bilayers clearly demonstrates such potentiality and feasibility for the near future. Amongst the exotic properties appearing in and at the surface of such quantum materials, spin-momentum locking (SML) and Rashba-Edelstein effects remain as key ingredients to effectively convert the spin degree of freedom into a charge or a voltage signal. In this work, we extend our analyses to the quantification of orbital momentum-locking and related orbital charge conversion effects in Bi_{0.85}Sb_{0.15} via orbital Rashba-Edelstein effects. In that sense, we will provide some clear theoretical and numerical insights implemented by multi-orbital and multi-layered tight-binding methods (TB) to clarify our recent experimental results obtained by THz-TDS spectroscopy.