Direct observation of nanometer-scale orbital angular momentum accumulation

TL;DR

This study directly observes nanometer-scale orbital angular momentum accumulation caused by the orbital Hall effect in titanium thin films, using electron energy-loss spectroscopy to measure orbital accumulation at edges.

Contribution

It provides the first direct measurement of orbital accumulation due to the orbital Hall effect with nanometer resolution.

Findings

Orbital accumulation detected at titanium film edges.

Orbital diffusion length approximately 7.3 nm.

Orbital diffusion length depends on nanostructure morphology.

Abstract

Conversion of charge to orbital angular momentum through the orbital Hall effect (OHE) holds transformative potential for the development of orbital-based electronics, however, it is challenging to directly observe the electrically generated orbital accumulation. Here, we detect the OHE by directly quantifying the orbital accumulation along the edges of a titanium thin film using a scanning transmission electron microscope. We measure the Ti L-edge using electron energy-loss spectroscopy with nanometer resolution and find a sizable orbital accumulation at the sample's outer perimeters, consistent with all signatures expected for the OHE, and determine an orbital diffusion length $\ell_o \approx 7.3$ nm. Our data points to a surprising dependence of the orbital diffusion length on the nano-structural morphology.