Imaging Quantum Mechanical Effects in Superconductors with Polarized Neutrons

Macroscopic Quantum effects such as the Meissner effect and magnetic flux trapping in massive, pure poly-crystalline lead samples and in a low purity crystalline sample having non-superconducting parts could be visualized and quantified by radiography with polarized neutrons. A uniform poly-crystalline Pb sample with a high purity of 1−1×10−4 weight% and one with a low purity of approx. 85 weight% Pb having non-superconducting parts showed a partial Meissner effect and for Bext = 0 and T < Tc a non-uniform magnetic flux trapping. Based on radiographies with polarized neutrons the trapped and expelled magnetic fields could be calculated for the uniform lead sample, in the case of the sample which contains non-superconducting parts an asymmetric (also squeezed) field distribution yielded the best fit.