Magnetic-field tunable photonic stop band in the three-dimensional array of conducting spheres

TL;DR

This study demonstrates how the photonic stop band in a three-dimensional array of conducting spheres can be tuned by external magnetic fields, controlling the order-disorder transition and affecting electromagnetic transmission properties.

Contribution

We introduce a method to tune photonic crystal properties via magnetic-field-induced order-disorder transitions in a 3D array of conducting spheres, supported by experimental data and a predictive model.

Findings

Ordered state exhibits a clear stopband.

Disordered state shows nearly no stopband.

Model accurately predicts effects of magnetic field on fluctuations.

Abstract

We explore possibility of tuning photonic crystal properties via order-disorder transition. We fabricated a photonic bandgap material consisting of a three-dimensional array of conducting magnetizable spheres. The spheres self-assemble into ordered state under external magnetic field, in such a way that the crystalline order can be continuously controlled. We study mm-wave transmission through the array as a function of magnetic field, i.e. for different degrees of order. This was done for the regular crystal, as well for the crystal with the planar defect which demonstrates resonance transmission at a certain frequency. We observe that in the ordered, "crystalline" state there is a well-defined stopband, while in the completely disordered, glassy or "amorphous" state, the stopband nearly disappears. We relate the disappearance of the stopband in the disordered state to the fluctuations in the particle area density. We develop a model which predicts how these fluctuations depend on magnetic field and how they affect electrodynamic properties of the whole sample. The model describes our results fairly well.