Non-Equilibrium Orbital Transport in Terahertz Optorbitronics

TL;DR

This paper reviews terahertz optorbitronics, a technique using ultrafast laser pulses to observe and control orbital electron transport in nanoscale materials, promising advancements in energy-efficient electronics.

Contribution

It introduces terahertz optorbitronics as a novel method for real-time observation and manipulation of orbital currents, highlighting recent experimental findings and potential applications.

Findings

Orbital currents can travel tens of nanometres or decay within a few atomic layers.

Ultrafast measurements can distinguish orbital motion from spin transport.

Engineered materials like graphene and altermagnets can serve as tunable orbital current sources.

Abstract

Modern information technologies rely on controlling the flow of electrons through their charge and spin. A rapidly emerging alternative is to use the orbital motion of electrons, the way they circulate around atomic sites as a new carrier of information. This orbital angular momentum (OAM) could enable more energy-efficient devices and reduce reliance on scarce heavy elements, but how orbital currents are generated and transported, especially on ultrafast timescales, remains largely unknown. In this review, we introduce terahertz optorbitronics, an approach that uses ultrafast femtosecond laser pulses and terahertz radiation to observe orbital transport in real time. On timescales of quadrillionth of a second, this technique allows us to track how orbital currents are launched, propagate, and convert into electrical signals in nanoscale thin-film materials. Surprisingly, recent experiments have revealed conflicting pictures such as orbital currents may travel over tens of nanometres like ballistic waves or instead decay within just a few atomic layers, highlighting a fundamental unresolved question in the field. We explain how these ultrafast measurements can disentangle orbital motion from conventional spin transport, and we highlight new materials from engineered graphene to altermagnets, that could act as tunable sources of orbital currents. We also discuss how light, electrical gating, strain, and interface design can be used to actively control orbital transport and improve its conversion into usable electronic signals. By revealing orbital transport as a dynamic, non-equilibrium process, terahertz optorbitronics opens a new direction for nanoscale science, the one that could lead to faster, more efficient technologies operating beyond the limits of conventional spin-based electronics.