Angular Dependence of the Nonlinear Transverse Magnetic Moment ofYBa2Cu3O6.95in the Meissner State

The angular dependence of the nonlinear transverse magnetic moment of untwinned high-quality single crystals of ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.95}$ has been studied at a temperature of 2.5 K using a low frequency ac technique. The absence of any signature at angular period $2\pi /4$ is analyzed in light of the numerical predictions of such a signal for a pure $d_{x^2{-y}^2}$ order parameter with line nodes. Implications of this null result for the existence of a nonzero gap at all angles on the Fermi surface are discussed.