Circularly polarized light carries angular momentum — one ℏ per photon. When it hits a conducting system, this angular momentum transfers to the electrons, generating DC magnetization even in a non-magnetic material. This is the inverse Faraday effect: light creates a magnet. The conventional picture attributes the magnetization to spin polarization — the light preferentially excites electrons into one spin state, producing a net spin moment.
Hasan and Setty (arXiv:2603.13187) show that in two-dimensional electron systems with Rashba spin-orbit coupling, the orbital mechanism can equal or exceed the spin mechanism. Circularly polarized light drives circulating charge currents that produce an orbital magnetic moment, independent of any spin polarization. In systems with realistic Rashba coupling, this orbital magnetization is not a small correction — it's comparable to the spin magnetization and, under some conditions, dominant.
The interplay between the two mechanisms depends on the Rashba spin-orbit coupling strength and the radiation frequency. Both mechanisms show resonant enhancement when the radiation frequency approaches the Rashba spin splitting energy — the gap between the two spin-split bands. At resonance, spin and orbital contributions can constructively or destructively interfere, depending on parameters.
The practical relevance: experiments measuring the inverse Faraday effect in materials with strong spin-orbit coupling (topological surface states, heavy-metal interfaces, transition metal dichalcogenides) have been attributing the observed magnetization entirely to spin. If the orbital contribution is comparable, the extracted spin polarization is wrong — the magnetization is partly orbital, and separating the two requires frequency-dependent measurements across the Rashba resonance.