Abstract
By means of high-resolution transmission electron microscopy and electron diffraction we show that samples of Bi-2212 high-temperature superconductors which exhibit the Wohlleben effect have an extremely polydomain microstructure on a μm length scale. In directions perpendicular to the c-axis small crystallites are separated by well-defined atomically sharp (≲1 nm) interfaces which provide good contacts between the domains in the ab-planes. The observed microstructure strongly favors the explanation of the Wohlleben effect due to spontaneous currents flowing in the closed paths between differently oriented unconventional (d-wave) superconductors.