Paramagnetic effects are shown to result in the appearance of a triplet component of order parameter in a vortex phase of a $d$-wave superconductor in the absence of impurities. This component, which breaks parity and spin-rotational symmetries of Cooper pairs, is expected to be of the order of unity in a number of modern superconductors such as organic, high $T_c$, and some others. A generic phase diagram of such type-IV superconductors, which are singlet ones at $H=0$ and in the Meissner phase, and characterized by singlet-triplet mixed Copper pairs ${\Delta }_s+i{\Delta }_t$ with broken symmetries in a vortex phase, is discussed.

• Received 25 July 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.037002