We show that spin-orbit coupling (SOC) in InSe enables the optical transition across the principal band gap to couple with in-plane polarized light. This transition, enabled by $p_{x,y}\leftrightarrow p_z$ hybridization due to intra-atomic SOC in both In and Se, can be viewed as a transition between two dominantly $s$- and $p_z$-orbital based bands, accompanied by an electron spin-flip. Having parametrized $\mathbf{k}·\mathbf{p}$ theory using first-principles density functional theory we estimate the absorption for ${\sigma }^{\pm }$ circularly polarized photons in the monolayer as $\sim 1.5$%, which saturates to $\sim 0.3$% in thicker films (3–5 layers). Circularly polarized light can be used to selectively excite electrons into spin-polarized states in the conduction band, which permits optical pumping of the spin polarization of In nuclei through the hyperfine interaction.

中文翻译：

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单层和多层InSe中的自旋轨道耦合，光学跃迁和自旋泵浦

我们显示InSe中的自旋轨道耦合（SOC）可以使跨主带隙的光学跃迁与平面内偏振光耦合。此过渡由$p_{X，ÿ}\leftrightarrow p_{ž}$ In和Se中由于原子内SOC引起的杂化可以看作是两个主要分子之间的过渡 $s$- 和 $p_{ž}$轨道带，并伴有电子自旋翻转。参数化$\mathbf{ķ}·\mathbf{p}$ 使用第一原理密度泛函理论的理论，我们估计了 ${\sigma }^{\pm }$ 单层中的圆偏振光子为 $〜1.5$％，饱和到 $〜0.3$％在较厚的薄膜（3-5层）中。圆偏振光可用于选择性地将电子激发成导带中的自旋极化态，从而允许通过超精细相互作用对In原子核的自旋极化进行光泵浦。