To understand superconductors, researchers explore their behavior at the limits of superconductivity, such as at high temperature or under strong magnetic field. New experiments investigate superconductivity at the limits of thickness, finding unexpected vortex behavior in ultrathin films [1]. Using a high-resolution magnetic imaging technique, Nofar Fridman from the Hebrew University of Jerusalem and colleagues measured vortex sizes in superconducting samples of various thicknesses and found larger-than predicted vortices in films made up of six or fewer atomic layers. The results suggest that thin superconductors host two superconducting states: one in the bulk of the material, the other confined to the surface layers. This behavior challenges our present understanding of how superconductors behave.
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