Third-Harmonic Susceptibility in Single-Crystal YBa₂Cu₃O_7-x Thin Films

Abstract

Higher-harmonic susceptibility was investigated for single-crystal YBa 2 Cu 3 O 7- x thin films located in the ac magnetic field perpendicular to the film plane. We found for the first time that the third-harmonic term of the thin films has nonzero values in the region of ac-susceptibility transition. The nonlinear response against ac magnetic field indicates that the Maxwell-Strongin model is not applicable and there must be some mechanism obstructing the vortex motion in the films.