Abstract
Topological transition of the iso-frequency contour (IFC) from a closed ellipsoid to an open hyperboloid provides unique capabilities for controlling the propagation of light. However, the ability to actively tune these effects remains elusive, and the related experimental observations are highly desirable. Here, a tunable electric IFC in a periodic structure composed of graphene/dielectric multilayers is investigated by tuning the chemical potential of the graphene layer. Specially, we present the actively controlled transportation in two kinds of anisotropic zero-index media containing perfect electric conductor/perfect magnetic conductor impurities. Finally, by adding variable capacitance diodes into a two-dimensional transmission-line system, we present an experimental demonstration of the actively controlled magnetic topological transition of dispersion based on electrically controllable metamaterials. With the increase in voltage, we measure the different emission patterns from a point source inside the structure and observe the phase-transition process of IFCs. The realization of an actively tuned topological transition will open up a new avenue in the dynamical control of metamaterials.
Highlights
Hyperbolic metamaterials (HMMs) have attracted great attention due to their open iso-frequency contour (IFC) in the wave vector space
By actively changing the chemical potential of the graphene layer, two special cases corresponding to two kinds of anisotropic ε-near-zero (ENZ) media can be realized in the proposed structure at a fixed frequency
To observe the influence of the topological transition on the wave propagations, we study the transmission property of the two kinds of ENZ media embedded with a perfect electric conductor (PEC) or perfect magnetic conductor (PMC) defect
Summary
Hyperbolic metamaterials (HMMs) have attracted great attention due to their open iso-frequency contour (IFC) in the wave vector space. By tuning the chemical potential of the graphene layer, we theoretically analyze and numerically simulate the tunable emission patterns in a periodic structure composed of graphene/dielectric multilayers. By actively changing the chemical potential of the graphene layer, two special cases corresponding to two kinds of anisotropic ε-near-zero (ENZ) media can be realized in the proposed structure at a fixed frequency.
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