A crystal made entirely of electron pairs has been found floating inside a liquid of single particles.
April 29, 2026
Original Paper
Uncovering Exotic Paired States in the 2D Spin-Imbalanced Fermi Gas with Neural Wave Functions
arXiv · 2604.24883
The Takeaway
Spin-imbalanced Fermi gases exhibit a strange state of matter where some particles pair up while others remain solitary. These Cooper pairs typically flow like a liquid to create superconductivity, but here they lock into a rigid crystalline structure instead. This exotic arrangement occurs at intermediate interaction strengths that were previously poorly understood. This discovery proves that the building blocks of superconductivity can behave like solid ice even while surrounded by a sea of fluid. Understanding these rigid pair states helps researchers design new materials with tailored quantum properties for more efficient energy transport.
From the abstract
We study the zero-temperature phase diagram of the 2D spin-imbalanced Fermi gas with short-ranged attractive interactions using the recently developed neural network variational Monte Carlo method with the AGPs FermiNet Ansatz. The Fulde-Ferrell-Larkin-Ovchinnikov phase is observed in the weakly interacting BCS limit and a polarised superfluid is seen in the strongly interacting BEC limit. When the interactions are strong, the minority-spin momentum density is reduced almost to zero in the momen