Laser-induced torques in metallic antiferromagnets

We study laser-induced torques in the antiferromagnet ${\mathrm{Mn}}_2\mathrm{Au}$. We find that even linearly polarized light may induce laser-induced torques in ${\mathrm{Mn}}_2\mathrm{Au}$; that is, the light does not have to be circularly polarized. The laser-induced torques in ${\mathrm{Mn}}_2\mathrm{Au}$ are comparable in magnitude to those in the ferromagnets Fe, Co, and FePt at optical frequencies. We also compute the laser-induced torques at terahertz (THz) frequencies and compare them to the spin-orbit torques (SOTs) excited by THz laser pulses. We find the SOTs are dominant at THz frequencies for the laser-field strengths used in experiments. Additionally, we show that the matrix elements of the spin-orbit interaction (SOI) can be used to add SOI only during the Wannier interpolation, which we call Wannier interpolation of SOI. This technique allows us to perform the Wannier interpolation conveniently for many magnetization directions from a single set of Wannier functions.

Figure 1

Laser-induced torque in ${\mathrm{Mn}}_2\mathrm{Au}$ vs quasiparticle broadening $\mathrm{\Gamma }$ when the Néel vector points in the 110 direction. Comparison between the results obtained within the WISOI approach (solid lines) and the results obtained based on MLWFs that include SOI (dashed lines). The torque is shown in units of yJ = yoctojoule = ${10}^{-24}$ joule.

Figure 2

Laser-induced torque in ${\mathrm{Mn}}_2\mathrm{Au}$ vs azimuthal angle $\varphi$ when the polar angle is $\theta ={90}^{\circ }$ and when $\mathrm{\Gamma }=25$ meV.

Figure 3

Laser-induced torque in ${\mathrm{Mn}}_2\mathrm{Au}$ vs quasiparticle broadening $\mathrm{\Gamma }$ when the staggered magnetization is along (100), i.e., $\widehat{\mathcal{L}}={\widehat{\mathit{e}}}_x$, and when $\mathit{\epsilon }=({\widehat{\mathit{e}}}_x+{\widehat{\mathit{e}}}_z)/\sqrt{2}$, i.e., $\mathit{\epsilon }\parallel \left(101\right)$.

Figure 4

Laser-induced torque in ${\mathrm{Mn}}_2\mathrm{Au}$ vs quasiparticle broadening $\mathrm{\Gamma }$ when the staggered magnetization is along (001), i.e., $\widehat{\mathcal{L}}={\widehat{\mathit{e}}}_z$.

Figure 5

Laser-induced torque in ${\mathrm{Mn}}_2\mathrm{Au}$ vs azimuthal angle $\varphi$ when the polar angle is $\theta ={90}^{\circ }$ and when $\mathrm{\Gamma }=25$ meV.