QMUL Scientists Uncover Shape-Proof Pathway to Exotic Electrical Behaviour
EECS researchers from the Centre for Electronics have reported a fresh theoretical result that settles a long-standing question in materials physics.
Their new study shows that a key set of calculations used to test whether a crystal could exhibit negative static electric susceptibility remains stable no matter what macroscopic shape the sample takes.
Negative static susceptibility is an unusual and still largely theoretical property in which a material would respond to an applied electric field in the opposite direction to what is normally expected. It has been proposed as a route to future metamaterials and advanced electromagnetic devices, but testing its feasibility requires rigorous mathematical tools. Until now, many of these tools gave different answers depending on whether a crystal was imagined as a slab, a sphere or a needle.
The QMUL team focused on what is known as the finite crystal method. They found that its bounds on susceptibility stay consistent even when tested across various crystal structures and a wide range of sample geometries. This contrasts with older approaches that shifted results dramatically when the sample shape changed. The work also highlights spheres and rhombohedra as especially reliable shapes for evaluating these bounds.
Lead author Rahul Dutta said the findings offer clarity that has been missing from the field. "Researchers have been debating these shape-dependent effects for years. Our work shows that with the right method, the bounds are robust. This gives us a more dependable foundation for exploring unusual electrical responses in engineered materials," he said.
The study strengthens QMUL's position in the fundamental science that underpins next-generation electromagnetics and provides a cleaner path forward for anyone investigating whether exotic material responses are theoretically achievable.