Inducing and controlling rotation on small objects using photonic topological materials

TL;DR

This paper demonstrates how magnetic fields can control Casimir torques on photonic topological insulator surfaces, enabling in situ rotation of small objects through nonreciprocal surface modes.

Contribution

It introduces a tunable, magnetic-field-dependent Casimir torque on photonic topological insulators, revealing a unique 2π periodicity and enabling external control of object rotation.

Findings

Casimir torque exhibits 2π periodicity due to nonreciprocal surface modes.

Magnetic field can externally control the torque's direction and magnitude.

Potential applications in nano-opto-mechanical systems.

Abstract

Photonic topological insulator plates violate Lorentz reciprocity which leads to a directionality of surface-guided modes. This in-plane directionality can be imprinted via an applied magnetic field. On the basis of macroscopic quantum electrodynamics in nonreciprocal media, we show that two photonic topological insulator surfaces are subject to a tuneable, magnetic-field dependent Casimir torque. Due to the directionality, this torque exhibits a unique $2\pi$ periodicity, in contradistinction to the Casimir torques encountered for reciprocal uniaxial birefringent media or corrugated surfaces which are $\pi$-periodic. Remarkably, the torque direction and strength can be externally driven in situ by simply applying a magnetic field on the system, and we show that this can be exploited to induce a control the rotation of small objects. Our predictions can be relevant for nano-opto-mechanical experiments and devices.