Anisotropic spin motive force in multi-layered Dirac fermion system, $\alpha$-(BEDT-TTF)${}_2$I${}_3$

We investigate the anisotropic spin motive force in $\alpha$-(BEDT-TTF)${}_2$I${}_3$, which is a multi-layered massless Dirac fermion system under pressure. Assuming the interlayer antiferromagnetic interaction and the interlayer anisotropic ferromagnetic interaction, we numerically examine the spin ordered state of the ground state using the steepest descent method. The anisotropic interaction leads to the anisotropic spin ordered state. We calculate the spin motive force produced by the anisotropic spin texture. The result quantitatively agrees with the experiment.