THE PHASE-TRANSITION PHENOMENA IN ANISOTROPIC SUPERCONDUCTORS - EFFECT OF THE ORTHORHOMBIC CRYSTAL-FIELD AND THE POTENTIAL IMPURITY SCATTERING

A combined effect of the orthorhombic crystal field and potential impu rity scattering on several superconducting states of a tetragonal symm etry is studied within a weak-coupling mean field approach. It is show n that the nonmagnetic impurities stabilize the states belonging to th e identity irreducible representation, The electronic specific heat ju mp at the phase transition is analyzed. Its dependence on the potentia l scattering rate for large impurity concentration is shown to be rema rkably different for the states with a nonzero value of the Fermi surf ace averaged order parameter than for those with a vanishing one. In p articular, very distinct signals from d(x2-y2) state in YBCO and d(xy) state in BSCCO compound are predicted. This effect may be used as a t est for the presence of these states in the above cuprates.