We have applied the mutual inductive method to study higher-order harmonics
of complex ac susceptibility χn=χn′−iχ"n for
YB_2C_3O_{7-\delta}thinfilmsasfunctionofthetemperatureandtheappliedfield.TheexperimentalresultswerecomparedwithanalyticalandnumericalresultsobtainedfromtheIshida−Mazakimodelandthesolutionoftheintegralequationforthecurrentdensity,respectively.Bothmodelsallowustoreproducedthemainexperimentalfeatures,however,asnincreasesthenumericalmodelshowsnotablediscrepancies.Thisfailurecanbeattributedtothecurrent−voltagecharacteristics.AlsothisinvestigationyieldstheactivationenergyU_candthecriticalcurrentdensityJ_c$ for two samples
both at T=0.Comment: 8 pages, 3 figure