Direct probe of the interior of an electric pion in a Cooper pair superinsulator

The nature of hadrons is one of the most fundamental mysteries of physics. It is generally agreed that they are made of “colored” quarks, which move nearly free at short scales but are confined inside hadrons by strong interactions at large distances. Because of confinement, quarks are never directly observable and, experimentally, their properties can be tested only indirectly, via high energy collisions. Here we show that superinsulating films realize a complete, one-color model system of hadron physics with Cooper pairs playing the role of quarks. We report measurements on highly controlled NbTiN films that provide a window into the interior of "Cooper pair mesons" and present the first direct evidence of asymptotic freedom, ‘t Hooft’s dual superconductivity confinement mechanism, and magnetic monopoles. Quarks in the interior of hadrons make up most of ordinary matter, yet their observation is not possible, and their properties can only be probed indirectly. Adopting an analogy between physics of superinsulators and high energy physics, the authors present direct observations of the interior of electric mesons made of Cooper pairs by standard transport measurements.