In-plane optically tunable magnetic states in 2D materials via tailored femtosecond laser driving

It is well established that light can control magnetism in matter, e.g. via the inverse Faraday effect or ultrafast demagnetization. However, such control is typically limited to magnetization transverse to light’s polarization plane, or out-of-plane magnetism in 2D materials, while in-plane magnetic moments have remained largely unexplored. This is due to the difficulty of generating electronic orbital angular momentum components within light’s polarization plane. Here we overcome this limitation, demonstrating complete three-dimensional, all-optical control of magnetism in 2D materials. Using first-principles simulations, we show that a tailored, two-color laser field can induce and steer magnetic moments in any direction with the relative angle between the laser polarizations playing a key parameter in coherent control. We analyze the physical mechanism of this process and show that it arises from a simultaneous breaking of time-reversal and spatial-inversion symmetries in the two-color laser. In-plane orbital moments are introduced via non-zero out-of-plane longitudinal photogalvanic currents enabled by broken inversion and mirror symmetries, while time-reversal symmetry breaking enables build-up of spin-rotation processes through spin-orbit coupling, translating the orbital moments to transient magnetism. Our findings demonstrate a full 3D coherent control scheme for transient magnetic states on femtosecond timescales driven by tailored lasers, and can be used to develop novel spectroscopies for magnetism, all-optical magnetic switching for ultrafast spintronics, and novel information storage capabilities.

💡 Research Summary

This paper presents a groundbreaking method for full three‑dimensional, all‑optical control of magnetism in two‑dimensional (2D) materials using a tailored two‑color femtosecond laser field. Conventional light‑induced magnetic phenomena—such as the inverse Faraday effect or ultrafast demagnetization—have historically been limited to generating magnetization perpendicular to the light’s polarization plane (i.e., out‑of‑plane, along the propagation direction). Consequently, in‑plane magnetic moments in 2D systems have remained largely inaccessible because ordinary light does not readily impart orbital angular momentum within its own polarization plane.

The authors overcome this limitation by employing a bichromatic laser configuration: a fundamental circularly polarized pulse at frequency ω₁ (400 nm wavelength) combined with its second harmonic (2 ω₁) linearly polarized along a controllable direction. The total vector potential is expressed as
A(t)=f(t)