Over-Barrier Photoelectron Emission with Rashba Spin-Orbit Coupling

TL;DR

This paper presents a theoretical model linking Rashba spin-orbit coupling strength to quantum efficiency in photoelectron emission, showing significant improvements in QE for strong RSOC materials and providing a tool for characterizing RSOC effects.

Contribution

The authors develop an analytical model that accurately describes QE dependence on RSOC strength, improving upon traditional models and enabling RSOC characterization in materials.

Findings

QE increases significantly with strong RSOC

Analytical scaling law enables RSOC strength extraction

Traditional models may substantially underestimate RSOC effects

Abstract

We develop a theoretical model to calculate the quantum efficiency (QE) of photoelectron emission from materials with Rashba spin-orbit coupling (RSOC) effect. In the low temperature limit, an analytical scaling between QE and the RSOC strength is obtained as QE $\propto (\hbar\omega-W)^2+2E_R(\hbar \omega-W) -E_R^2/3$, where $\hbar\omega$, $W$ and $E_R$ are the incident photon energy, work function and the RSOC parameter respectively. Intriguingly, the RSOC effect substantially improves the QE for strong RSOC materials. For example, the QE of Bi$_2$Se$_3$ and Bi/Si(111) increases, by 149\% and 122\%, respectively due to the presence of strong RSOC. By fitting to the photoelectron emission characteristics, the analytical scaling law can be employed to extract the RSOC strength, thus offering a useful tool to characterize the RSOC effect in materials. Importantly, when the traditional Fowler-Dubridge model is used, the extracted results may substantially deviate from the actual values by $\sim90\%$, thus highlighting the importance of employing our model to analyse the photoelectron emission especially for materials with strong RSOC. These findings provide a theoretical foundation for the design of photoemitters using Rashba spintronic materials.