Spin current, or the flow of spin angular momentum, is a central concept in spintronics. With rapid progress in this field, only one side of angular momentum, or spin, has received a lot of attention. The other side, or orbital angular momentum, has long been overlooked, owing to the conventional belief that it is quenched by crystal fields.

Recent theoretical and experimental studies have, however, challenged this view, demonstrating evidence of orbital Hall effect and the orbital Rashba–Edelstein effect. These findings establish that orbital currents play a fundamental role in angular momentum dynamics and open the door to a new field known as ‘orbitronics.’

Shedding new light on this emerging field, this review published in Journal of the Physical Society of Japan looks at the recent experimental progress in the field of orbitronics. It presents a comprehensive overview of orbital current generation mechanisms, including the orbital Hall effect and the orbital Rashba–Edelstein effect, using simple models, and discusses their experimental investigations.

The review also examines the dynamics of orbital and spin currents in ferromagnets, revealing that orbital currents can propagate over longer distances than spin currents. Furthermore, it discusses the interaction of orbital currents and magnetization, highlighting the role of spin-orbit coupling, orbital torque generation, and orbital pumping.

In addition, the review also explores recently discovered orbitronic phenomena, including the magneto-optical Kerr effect, orbital current-induced magnetoresistance, orbitronic THz emission, and thermal generation of orbital currents.

It also identifies key material classes for orbitronics, including transition metals, rare-earth elements, two-dimensional materials, and oxides. Notably, orbital currents can be generated in a wider range of materials than spin currents.

Overall, these findings show that orbital contributions to spintronic phenomena are non-negligible. Going ahead, orbital currents offer potential for the development of energy-efficient next-generation memory devices, and the emerging field of orbitronics can play a key role in future information-processing technologies.

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