Tunable self-assembled Casimir microcavities and polaritons

Gold nanoflake pairs form by self-assembly in an aqueous ligand solution and offer stable and tunable microcavities by virtue of equilibrium between attractive Casimir forces and repulsive electrostatic forces. Spontaneous formation of ordered structures-self-assembly-is ubiquitous in nature and observed on different length scales, ranging from atomic and molecular systems to micrometre-scale objects and living matter(1). Self-ordering in molecular and biological systems typically involves short-range hydrophobic and van der Waals interactions(2,3). Here we introduce an approach to micrometre-scale self-assembly based on the joint action of attractive Casimir and repulsive electrostatic forces arising between charged metallic nanoflakes in an aqueous solution. This system forms a self-assembled optical Fabry-Perot microcavity with a fundamental mode in the visible range (long-range separation distance about 100-200 nanometres) and a tunable equilibrium configuration. Furthermore, by placing an excitonic material in the microcavity region, we are able to realize hybrid light-matter states (polaritons(4-6)), whose properties, such as coupling strength and eigenstate composition, can be controlled in real time by the concentration of ligand molecules in the solution and light pressure. These Casimir microcavities could find future use as sensitive and tunable platforms for a variety of applications, including opto-mechanics(7), nanomachinery(8) and cavity-induced polaritonic chemistry(9).

Automated summary

This study introduces a method for stable microcavity formation based on self-assembly of gold nanoflake pairs in an aqueous solution, utilizing the equilibrium between attractive Casimir forces and repulsive electrostatic forces. The system allows for tunable optical microcavities with adjustable equilibrium configurations, enabling the realization of hybrid light-matter states. These Casimir microcavities could potentially be used in opto-mechanics, nanomachinery, and cavity-induced polaritonic chemistry.