Rectification of Spin Current in Inversion-Asymmetric Magnets with Linearly Polarized Electromagnetic Waves

We theoretically propose a method of rectifying spin current with a linearly polarized electromagnetic wave in inversion-asymmetric magnetic insulators. To demonstrate the proposal, we consider quantum spin chains as a simple example; these models are mapped to fermion (spinon) models via Jordan-Wigner transformation. Using a nonlinear response theory, we find that a dc spin current is generated by the linearly polarized waves. The spin current shows rich anisotropic behavior depending on the direction of the electromagnetic wave. This is a manifestation of the rich interplay between spins and the waves; inverse Dzyaloshinskii-Moriya, Zeeman, and magnetostriction couplings lead to different behaviors of the spin current. The resultant spin current is insensitive to the relaxation time of spinons, a property of which potentially benefits a long-distance propagation of the spin current. An estimate of the required electromagnetic wave is given.

Figure 1

Noncentrosymmetric spin chains considered in this work. Schematic picture of (a) a dimerized spin chain and (b) an antiferromagnet of weakly coupled spin chains in a staggered magnetic field. The model consists of two magnetic atoms with different $g$ factor and alternating bonds. Band structure of Jordan-Wigner fermions for (c) $\delta =h_s/J=0$, and (d) $\delta =1/3$, and $h_s/J=1/10$.

Figure 2

Frequency dependence of the nonlinear conductivity ${\sigma }^{(2)}(\omega )$ for $J=1$, $\delta =1/3$, and $h_s=1/10$. Panels (a)–(c) are the results for $\tau \to \infty$ with (a) inverse Dzyaloshinskii-Moriya coupling with $p=1$, (b) Zeeman coupling, and (c) magnetostriction effect with $A=x$ and $A_s=1-x$. Different lines in (a) and (c) are the results for different ratio of parameters $p_s/p$ and $A/B$, respectively. Panels (d)–(f) show the $\tau$ dependence of (d) inverse DM coupling with $p=1$ and $p_s=0.2$, (e) Zeeman coupling, and (f) magnetostriction effect with $A=1/3$ and $A_s=2/3$.