Mechanism for magnetic-flux generation in grain boundaries ofYBa2Cu3

Abstract

The spontaneously generated magnetic flux observed by Mannhart et al. in asymmetric 45°grain boundaries in YBa 2 Cu 3 O 7Ϫx was explained by them in terms of a d x 2 Ϫy 2 superconducting order parameter and grain boundary faceting. This article argues that twin boundaries which contact the grain boundary also play an important role. ͓S0163-1829͑96͒05242-3͔

Review: grain boundary faceting–roughening phenomena

“…The interfacial atomic structure which includes atoms common to both crystals should be conductive to a limited decrease in the order parameter. However, the presence of pseudo-periodic microfacets, with a size comparable to the vortex core, should induce an efficient pinning of the magnetic flux [223,227,228,[239][240][241][242][243]. From these structural data, and in agreement with measurements on specific coincidence boundaries, it is inferred that the critical current in cuprate ceramics is likely to be increased, if one could markedly enhance the ratio of coincidence boundaries which do not contain the (a, b) plane (Fig.…”

Induced paramagnetic states by localizedπloops in grain boundaries

“…Small β π-loops could be likely localized between GBs with different orientation along a junction [21] or where faceting cause an imperfect not completely flat GB passing from a conventional junction to a π-junction or viceversa. Recently also engineered "zigzag" arrays of mixed π/conventional junctions have been realized and mea-sured [22,23].…”