Manipulating the arrangement of atoms offers new possibilities for controlling how light interacts with matter. Complex topological defects, known as exceptional points, are maintained within atomic arrays even under conditions previously thought impossible. Investigations in Taiwan showed that these features survive strong magnetic fields while continuously deforming two-dimensional arrangements of subwavelength atoms from square to triangular lattices.

Specific defects in atomic arrangements, called exceptional points, endure even with strong external forces applied via magnetic fields. These features, typically disrupted by such conditions, maintained themselves while simultaneously changing the shape of two-dimensional atom arrays from square to triangular forms. This stability arises because interactions between atoms become particularly pronounced at what is known as the light cone; this effect prevents the complete removal of these topological structures.

An unexpected stability exists within arrangements of atoms, maintaining complex topological defects, exceptional points, even under strong magnetic fields. This resilience stems from atomic interactions becoming particularly pronounced at the light cone; imagine shining a torch into darkness, where the light cone defines the boundary beyond which no information escapes, creating intense focus within this atomic system.

An exceptional point can be likened to a balancing point on a seesaw where even a small disturbance causes significant change, representing both instability and potential for unique responses. The team details how these arrangements respond to increasing external forces, opening avenues for novel material design.

Exceptional Points Persist Under Magnetic Fields via Lattice Geometry Control

Maintaining topological defects within atomic arrays has proven challenging under strong magnetic fields. At the Institute of Atomic and Molecular Sciences, in collaboration with multiple institutions, exceptional points now survive magnetic fields up to a point where they approach the ‘light cone’. Previously, such features were expected to be removed by sufficiently powerful external forces in bounded systems; however, lattice geometry manipulation revealed their durability.

Specifically, increasing the magnetic field merely drives these exceptional points toward the light cone, defining intense focus within the system, without causing their annihilation when lattices undergo continuous square-to-triangular deformation. Skin localization, the tendency of modes to accumulate at edges, responded unpredictably to changing fields exhibiting bipolar accumulation at opposite boundaries with intermediate strengths before suppressing itself entirely.

Geometric Lattice Modulation Stabilises Topological Exceptional Points in Two Dimensions

Continuous square-to-triangular lattice deformation proved key for stabilising these delicate topological features; this technique systematically alters atomic interactions within the array allowing observation of how exceptional points respond under stress. This reshaping drives the system through different phases characterised by band Chern numbers, fingerprints revealing electron flow and swirl throughout the material. Careful control over geometric transition alongside an applied magnetic field enabled manipulation of atom arrangement without destroying fragile exceptional points, something previously thought impossible. Changes to skin localization provide further insight into how external forces affect energy distribution at boundaries.

Sustaining Strong Exceptional Points Despite External Magnetic Fields

The team’s success in sustaining these delicate topological features challenges a long-held belief that strong external forces inevitably destroy exceptional points within bounded systems. Prior work suggested such defects were fundamentally unstable under Hermitian fields; however, increasing magnetic field strength does not immediately eliminate them but relentlessly drives them towards the light cone, defining intense focus within the atomic arrangement. This offers new avenues for controlling light and matter at nanoscale dimensions by exploiting this unexpected durability against destabilising forces.

A two-dimensional array of atoms was investigated with their positioning manipulated using continuous change from square to triangular lattices alongside an applied magnetic field. Lattice geometry and magnetism were carefully controlled while focusing on regions exhibiting band Chern numbers of (2,-2) before transitioning into gapless exceptional areas. Topological defects can endure even as magnetic fields increase, challenging expectations regarding inherent instability under such conditions; it reveals how manipulating atom positions allows preservation of these features despite external influence. By continuously reshaping a square lattice into a triangular form whilst applying magnetism, these features moved closer to the light cone, defining intense focus within the system, without disappearing entirely. This durability arises from unique interactions between atoms and opens possibilities for engineering materials with tailored responses to both light and external forces through this controlled manipulation of atomic arrangements.

The researchers demonstrated that exceptionally stable topological defects, called exceptional points, can be sustained in a two-dimensional array of subwavelength atoms even when subjected to increasing magnetic fields. Previously, such points were thought to be destroyed by strong Hermitian fields; however, increased field strength instead drove them towards the ‘light cone’ rather than eliminating them.

These findings establish how manipulating lattice geometry alongside magnetism allows preservation of these features despite external influence, offering new ways to control energy distribution at boundaries. The team reshaped square lattices into triangular forms while applying varying magnetic fields to observe this effect.

👉 More information
🗞 Exceptional Topology Survives Strong Hermitian Fields in Radiative Atomic Arrays
✍️ Tian-Shu Gou, Yi-Cheng Wang, Ya-Tang Yu, Guin-Dar Lin, Jhih-Shih You and H. H. Jen
🧠 ArXiv: https://arxiv.org/abs/2609.17313

More like this