Superconductors of mixed order-parameter symmetry in a Zeeman magnetic field

We study the effect of a Zeeman magnetic field in the superconducting phase with a two-component order-parameter scenario, such as d(x2)-(y2) + e(i theta) alpha, where alpha = d(xy), s. This scenario is equivalent to applying a magnetic field parallel to the Cu-O plane. In a weak magnetic field, which does not cause much change to the predominant d wave, it supresses the minor a component leading to pure d-wave phase. This observation is contrary to the effect of a magnetic field applied in the c direction to the Cu-O planes that are believed to induce a minor component a to d-wave superconductors. We also show that the response of such superconductors to a weak Zeeman magnetic field can be quite different depending on the phase theta of the minor component (alpha). [S0163-1829(99)01929-3].