Magnetic Field Dependence of Lambda in YBa₂Cu₃O_6.95: Results as a Function of Temperature and Field Orientation
C.P. Bidinosti, W.N. Hardy, D.A. Bonn, Ruixing Liang
Published in PRL: Phys. Rev. Lett., 83, 3277 (1999).

We present measurements of the magnetic field dependence of the penetration depth Lambda(H) for an untwinned YBa₂Cu₃O_6.95 single crystal for temperatures from 1.2 to 7 K in dc fields up to 177 G and directions 0º, ±45º and 90º with respect to the crystal b axis. The edges of the platelet sample have been polished round to limit extrinsic effects related to flux penetration. At the lowest temperature Delta_Lambda(H) in the a- and b-directions could be interpreted as agreeing with the Yip and Sauls prediction for the nonlinear Meissner effect in a d-wave superconductor. However, the systematics versus temperature and orientation, a key aspect of the theory, do not agree, and we conclude that the nonlinear Meissner effect is suppressed by a factor of order 10 or larger.