Valley Photonic Molecular Crystals

Abstract Organic topological insulators based on molecular crystals have attracted increasing attention for its novel topological phase and application potential for spintronics, valleytronics and flexible electronics. Unlike inorganic crystals, molecules in molecular crystals possess rotational degrees of freedom, which significantly influence the absorption, photonic and mechanical properties of molecular crystals. However, it is still a challenge to investigate the topological property after considering the molecular rotation, as rotation can disrupt the periodicity of the molecular crystal, rendering the traditional energy band theory inapplicable. Consequently, molecular rotation is often neglected in previous works. It is essential to address such impact, since it could enable the dynamic evolution of topological states and establish molecular rotation as a new degree of freedom for topological manipulation. In this work, we have employed the valley photonic crystal to theoretically and experimentally investigate the valley topological properties of molecular crystals under various rotational disorders, named as Valley Photonic Molecular Crystals (VPMC). We demonstrated that the topological properties of VPMC are preserved even under strong rotational disorder, highlighting their inherent robustness. The VPMC provides an excellent platform for emulating and investigating the topological properties of molecular crystals as it is feasible to fabricate and manipulate the rotation. Moreover, this work also opens up possibilities for device applications based on rotational disorder.