Fig. 1: Light control of magnetic interactions and magnetism via dissipation.
a In the absence of light, the interaction between the local spins (thick blue arrow) is reciprocal. The spins are driven towards the equilibrium configuration [alignment in the ferromagnetic case illustrated here] through a magnetic friction called the Gilbert damping (green arrows). b When the light is tuned to a frequency hν that selectively activates the red spin [in the way illustrated in Fig. 3], the light-induced torque (pink arrows) acts on the activated spin. As a result, the two spins effectively interact non-reciprocally, where the active (inactive) spin tries to anti-align (align) with the opponent’s spin. c Phase diagram of a layered ferromagnet under light injection, determined by our meanfield description (Eq. (8)). Here, the two ferromagnetic layers (A and B) are separated by a non-magnetic metal and the laser is injected to introduce active dissipation to the B layer at rate γB, making the interlayer magnetic interactions non-reciprocal. When the light is off (γB = 0), the magnetization of the two layers aligns for ferromagnetic interlayer interaction jAB(=jBA) > 0 (blue region). As the light-induced dissipation is turned on γB > 0, the system exhibits a phase transition to an antialigned configuration (red) at γB ≃ αB∣gB∣ and a non-reciprocal phase transition to a time-dependent chiral phase [where the two magnetizations exhibit many-body chase-and-runaway dynamics](cyan). [See text and Fig. 5 for further details.] We set the intralayer interaction and Gilbert damping of the layer A (B) as jAA = 10meV(jBB = 5meV) and αA = 0.1(αB = 2 × 10−3), respectively. The sd coupling strength for B is gB = − 10meV, the filling n = 1, and the temperature is kBT = 9meV. The dashed lines are the phase boundary at a lower temperature kBT = 5meV.
