This paper shows that shining two different laser colors on a thin, spin-textured magnet can produce a large out-of-plane spin and orbital accumulation. The effect appears in two-dimensional “unconventional” magnets that normally forbid such a response by symmetry. The authors report induced perpendicular Edelstein polarizations of order 0.5–1.5 μB (Bohr magnetons) when Rashba spin–orbit coupling is present and the system is driven by two light frequencies.

The work is theoretical. The researchers model a 2D Rashba magnet with a momentum-dependent magnetic order (they treat p-, d-, f-, and g-wave patterns). They include the light by shifting electron momentum with a time-dependent vector potential made of two polarized fields at frequencies ω and nω. In the high-frequency, off-resonant limit (roughly ℏω ≳ 1 eV in their treatment) they use a van Vleck expansion to get a simpler effective Hamiltonian for the driven, prethermal Floquet state. That effective model contains light-induced terms that act like a Zeeman field caused by the two-color interference.

At a conceptual level the key is symmetry breaking by the two-color drive. A single laser color preserves a twofold rotation symmetry (C2z) that forbids any net out-of-plane accumulation. Interference between the two frequencies, however, creates an in-plane Zeeman-like field whose direction and size depend on the relative phase, polarizations, amplitude ratio, and handedness of the beams. Because this in-plane field is generally misaligned with the crystal axes, it breaks C2z and allows a perpendicular Edelstein polarization (PEP) to appear. The authors trace the in-plane field to nonlinear single- and two-photon processes and to the interplay of Rashba coupling with the magnetic order.

The result matters because a perpendicular spin or orbital accumulation couples directly to magnetic order and can exert a torque that switches perpendicular magnetization without any external stray field. That is especially useful for compensated magnets, which have nearly zero net magnetization and therefore very small stray fields. In practice this mechanism could provide an all-optical, field-free route to write perpendicular magnetic memory bits, according to the authors.