Angular dependence of the nonlinear transverse magnetic moment of YBa2Cu3O6.95 in the Meissner state

The angular dependence of the nonlinear transverse magnetic moment of untwi nned high-quality single crystals of YBa2Cu3O6.95 has been studied at a tem perature of 2.5 K using a low frequency ac technique. The absence of any si gnature at angular period 2 pi/4 is analyzed in light of the numerical pred ictions of such a signal for a pure d(x)2(-y)2 order parameter with line no des. Implications of this null result for the existence of a nonzero gap at all angles on the Fermi surface are discussed.