Many experiments on high-temperature superconductors have shown paramagnetic behavior when the sample is field cooled. The paramagnetism was attributed to a d-wave order parameter creating pi-junctions in the samples. However, the same effect was later discovered in traditional low-temperature superconductors and conventional Josephson-junction arrays which are s wave. By simulating both conventional and mixed pi/conventional Josephson-junction arrays we determine that differences exist which may be sufficient to clearly identify the presence of pi junctions. In particular, the pi junctions cause a symmetry breaking providing a measurable signature of their presence.
The magnetic behavior of Multiply Connected Superconductors (MCS) can be described analyzing the simplest loop structures containing Josephson junctions: conventional loops with all conventional Josephson junctions and π-loops with an odd subset of πjunctions. These last are unconventional Josephson junctions in which the coupling has the reversed sign and appears in the ceramic materials as consequence of d-pairing. Among MCS the magnetic behavior of large β two-dimensional Josephson Junction Arrays (JJA) is based on the single loop behavior. Solving full mutual inductance Josephson junction square array equations with and without π-loops show that the mutual inductance coupling influence the distribution of π/conventional loops without altering substantially their single loop magnetization. The JJA mean magnetic behavior in low field can be recovered using a simple energy approach based on the single loop solutions avoiding the solution of the array full equations. Also we draw some consequences on the behavior of more complex MCS as high-T C ceramics and their observed paramagnetic susceptibilities (Paramagnetic Meissner Effect).
Annihilation cross-sections sigma(ann) for antineutrons on some nuclei (C, Al, Cu, Sn and Pb) at three antineutron momenta (180, 240 and 280 MeV/c) were measured at LEAR (CERN) with the OBELIX spectrometer. A behaviour sigma(ann) = = sigma0A(nu) has been found with nu almost-equal-to 2/3. The data are discussed following some models for antineutron-nucleus interaction
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