Linearly Polarized Few-Cycle Pulses Drive Carrier-Envelope Phase-Sensitive Coherent Magnetization Injection.

Circularly polarized light is well known to induce, or flip the direction of, magnetization in solids. At its heart, this arises from time-reversal symmetry breaking by the vector potential, causing inverse-Faraday or analogous physical effects. We show here that very short few-cycle pulses can cause similar phenomena even when they are linearly polarized and off resonant. We analyze the new effect with ab initio calculations and demonstrate that it similarly arises due to broken time-reversal symmetry and is carrier-envelope-phase (CEP) sensitive. Coherently tuning the CEP causes the induced magnetism to oscillate from zero to few percent Bohr magneton within few femtoseconds. By changing the laser angle and intensity, the magnetization sign and magnitude can be controlled. Remarkably, due to the nature of the physical mechanism that relies on spin-orbit interactions and orbital currents, the magnetization survives CEP averaging and the effect should be accessible even in the absence of CEP stabilization. Our Letter opens new routes for ultrafast coherent tuning and probing of magnetism and circumvents the need for circularly polarized driving or external magnetic fields.