| Summary: | The critical current density <i>J</i><sub>c</sub>, which is a maximum value of zero-resistivity current density, is required to exhibit not only larger value but also lower anisotropy in a magnetic field <i>B</i> for applications of high-<i>T</i><sub>c</sub> superconductors. Heavy-ion irradiation introduces nanometer-scale irradiation tracks, i.e., columnar defects (CDs) into high-<i>T</i><sub>c</sub> superconducting materials, which can modify both the absolute value and the anisotropy of <i>J</i><sub>c</sub> in a controlled manner: the unique structures of CDs, which significantly affect the <i>J</i><sub>c</sub> properties, are engineered by adjusting the irradiation conditions such as the irradiation energy and the incident direction. This paper reviews the modifications of the <i>J</i><sub>c</sub> anisotropy in high-<i>T</i><sub>c</sub> superconductors using CDs installed by heavy-ion irradiations. The direction-dispersion of CDs, which is tuned by the combination of the plural irradiation directions, can provide a variety of the magnetic field angular variations of <i>J</i><sub>c</sub> in high-<i>T</i><sub>c</sub> superconductors: CDs crossing at ±<i>θ</i><sub>i</sub> relative to the <i>c</i>-axis of YBa<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub> films induce a broad peak of <i>J</i><sub>c</sub> centered at <i>B</i> || <i>c</i> for <i>θ</i><sub>i</sub> < ±45°, whereas the crossing angle of <i>θ</i><sub>i</sub> ≥ ±45° cause not a <i>J</i><sub>c</sub> peak centered at <i>B</i> || <i>c</i> but two peaks of <i>J</i><sub>c</sub> at the irradiation angles. The anisotropy of <i>J</i><sub>c</sub> can also modified by tuning the continuity of CDs: short segmented CDs formed by heavy-ion irradiation with relatively low energy are more effective to improve <i>J</i><sub>c</sub> in a wide magnetic field angular region. The modifications of the <i>J</i><sub>c</sub> anisotropy are discussed on the basis of both structures of CDs and flux line structures depending on the magnetic field directions.
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