Focusing of micromechanical polaritons on topologically non-trivial hyperbolic metasurfaces

Dr. Johan Christensen, leader of the IMDEA Materials Institute’s Mechanical and Acoustic Metamaterials research group, is among the researchers behind a pioneering study exploring the topological properties of metamaterials.

This recent research, titled “Focusing of micromechanical polaritons on topologically non-trivial hyperbolic metasurfaces” and published in Advanced Materials, has attracted considerable attention due to its potential to revolutionize wave manipulation through the non-trivial and defect-immune characteristics inherent in topological metamaterials. The study was featured on the cover of the journal.

Topological metamaterials are distinguished by topological shielding of surface states, setting them apart from conventional materials. In the realms of acoustics and elasticity, these surface states manifest as localized vibrations at the interface between the metamaterial and its environment.

Unlike typical sound waves that propagate through the bulk of a material, these surface states are extremely robust, maintaining their properties even among small changes or imperfections in the material.

Dr. Christensen and his team have made remarkable progress by structuring the surfaces of elastic metamaterials with micrometer-sized pillars.

“This precise pattern that we have been able to achieve in this recent work includes specific symmetries designed to improve the performance of metamaterials,” explained Dr. Christensen.

“In particular, we were able to use both chiral and mirror symmetries to strengthen the stability of the topological states.”

Chiral symmetry, characterized by the property of objects or molecules that cannot be superimposed on their mirror image, and mirror symmetry, where objects look identical to their reflections, were both integral to the design.

“The precise arrangement of the pillars ensured the presence of these symmetries, greatly increasing the nature and elasticity of the topological states,” added Dr. Christensen.

Along with Dr. Christensen, researchers involved in the latest publication include Drs. Liyang Zheng from Carlos III University in Madrid and Prof. Minghui Lu from Nanjing University, China.

The research demonstrated the ability to focus highly directed ultrasound at low MHz therapeutic frequencies. This breakthrough, facilitated by the combination of chiral and mirror symmetry, achieved highly resilient performance and robustness to fabrication imperfections and disorders.