Metamaterials with index ellipsoids at arbitrary k-points.

Area of Science:

• Electromagnetism
• Materials Science
• Condensed Matter Physics

Background:

• Electromagnetic wave propagation is dictated by a medium's equifrequency surface.
• Conventional materials and metamaterials exhibit equifrequency surfaces centered at the zero k-point.
• Existing metamaterials often suffer from inherent bandwidth limitations.

Purpose of the Study:

• To propose and demonstrate a new class of metamaterials with multiple equifrequency ellipsoids.
• To explore the potential for broadband functionalities in these novel metamaterials.
• To investigate the role of global connectivity in determining metamaterial properties.

Main Methods:

• Designing metamaterials with interpenetrating metallic scaffolds to control momentum space properties.
• Analyzing the geometrical details influencing group velocities.
• Conducting microwave experiments to validate theoretical predictions.

Main Results:

• Demonstrated metamaterials with multiple index ellipsoids centered at arbitrary nonzero k-points.
• Established that the connectivity of metallic scaffolds dictates ellipsoid locations in momentum space.
• Confirmed broadband functionality, including negative refraction and orientation-dependent coupling.

Conclusions:

• The proposed metamaterials represent a new paradigm, distinct from resonant metamaterials.
• Global connectivity is a key factor for achieving broadband performance in metamaterials.
• These findings open avenues for advanced applications in optics and electromagnetics.