Chiral crystals consisting of microhelices have many optical properties, while presently available fabrication processes limit their large-scale applications in photonic devices. Here, by using a simplified simulation method, we investigate a bottom-up self-assembly route to build up helical crystals from the smectic monolayer of a colloidal helix racemate. With increasing the density, the system undergoes an entropy-driven cocrystallization by forming crystals of various symmetries with different helical shapes. In particular, we identify two crystals of helices arranged in binary honeycomb and square lattices, which are essentially composed of two sets of opposite-handed chiral crystals. Photonic calculations show that these chiral structures can have large complete photonic band gaps. In addition, in the self-assembled chiral square crystal, we also find dual polarization band gaps that selectively forbid the propagation of circularly polarized light of a specific handedness along the helical axis direction. The self-assembly process in our proposed system is robust, suggesting possibilities of using chiral colloids to assemble photonic metamaterials.

中文翻译：

---

胶体螺旋外消旋体的自组装手性光子晶体

由微螺旋组成的手性晶体具有许多光学性质，而目前可用的制造工艺限制了它们在光子器件中的大规模应用。在这里，通过使用简化的模拟方法，我们研究了自下而上的自组装路线，从胶体螺旋外消旋体的近晶单层构建螺旋晶体。随着密度的增加，该系统通过形成具有不同螺旋形状的各种对称的晶体而经历了熵驱动的共结晶。特别是，我们确定了排列成二元蜂窝状和方格子状的两个螺旋晶体，它们基本上由两组相反的手性晶体组成。光子计算表明，这些手性结构可以具有较大的完整光子带隙。另外，在自组装手性方形晶体中，我们还发现了双偏振带隙，该双偏振带隙有选择地禁止特定螺旋性的圆偏振光沿螺旋轴方向传播。我们提出的系统中的自组装过程很健壮，这表明使用手性胶体组装光子超材料的可能性。