Combined effect of flux pinning by three-directional columnar defects in a field-angular region of high-Tc superconductors

We investigated the combined effect of flux pinning by three-directional columnar defects (CDs) in a wide field-angular range of YBa2Cu3Oy thin films, where CDs parallel to the c-axis and CDs crossing at +/-theta(i) (theta(i) = 45 degrees, 60 degrees and 80 degrees) relative to the c-axis were installed by 200 MeV Xe-ion irradiations. The three-directional CDs with theta(i) <= +/- 60. form a field angular curve of critical current density J(c) with a broad peak centered at magnetic field (B) parallel to the c-axis, whereas the J(c) shows no peaks around the crossing angles of +/-theta(i). When the crossing angle is expanded to theta(i) = +/- 80 degrees, a drastic change in the field-angular behavior of J(c) is induced: there is not a large enhancement of J(c) around B parallel to c, but two large peaks of J(c) emerge at the two irradiation angles of theta(i) = +/- 80 degrees. We also demonstrated that the combined configuration consisting of CDs at theta(i) = 0 degrees, +/- 45 degrees, +/- 60 degrees and +/- 80 degrees provides a uniform enhancement of J(c) over a wide angular-region.