Beyond attraction: A novel approach to repulsive Casimir-Lifshitz forces using heterogeneous off-stoichiometry in gapped metals

We uncover a physical system that enables a switch between attractive and repulsive Casimir forces when a Teflon surface interacts with a new form of quantum material (i.e., gapped metal) surface across different liquid media. Past works usually suggest that entropic effects on the Casimir force (originating partly from its zero frequency contribution that has an approximately linear temperature dependence) occur at high temperatures and/or large separations. We propose a new way to achieve a zero-frequency Casimir effect, which reveals the potential for a Casimir force quantum switching within nanometer distances-a scale often thought to be unattainable. Furthermore, the heterogeneous surface can have different phases (both metallic and insulating). Hence, our results introduce a new method to induce phase (stoichiometry)-controlled attraction-repulsion transitions and to achieve quantum levitation in a liquid medium by tuning the liquid environment. This study opens up new possibilities for manipulating the Casimir interactions between surfaces, forming the basis for advancements in nanoscale technology.