Upper critical superconductivity field at a twin boundary

A theoretical investigation is reported of the superconducting properties of a twin boundary allowing for its finite transparency to conduction electrons. The temperature dependence of the upper critical field Hd (T) is calculated for the parallel orientation. The angular dependence of this field is considered in the range of small angles of inclination of the field to the boundary. A study is also made of the behavior of the magnetic moment and of the critical current near the Hd (T) curve. The finite transparency of a twin boundary gives rise to two phase transitions associated with the symmetry of a superconducting nucleus relative to the boundary