Paramagnetic and diamagnetic states in two-dimensional   Josephson-junction arrays
  Many experiments on high-temperature superconductors have shown paramagnetic behavior when the sample is field cooled. The paramagnetism was first 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 (or absence) of pi-junctions. In particular the pi-junctions cause a symmetry breaking providing a measurable signature of their presence in sample. 
Cinzia De Leo and Giacomo Rotoli (Dipartimento di Energetica and INFM,   L'Aquila, ITALY)