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AC response of the surface superconducting states of YB6 and ZrB12 single crystals in a swept magnetic field


  M.I. Tsindlekht[1]  ,   V.M. Genkin[1]  ,  G.I. Leviev[1]  ,  Y. Schlussel[1]  ,  I. Felner[1]  ,  V.B. Filippov[2]  ,  N.Yu. Shitsevalova[2]  
 [1] The Racah Institute of Physics, the Hebrew University of Jerusalem, Israel
[2] Institute for Material Science, NAS, Kyiv, Ukraine

We report the results of an experimental study of the low frequency ac response of the YB6 and ZrB12 single crystals in a swept magnetic field. The samples with dimensions 10 by 3 by 1 mm were inserted in the pick-up coil and the ac response at first, second, and third harmonic was measured over wide ranges of frequencies and sweep rates. We found that the second harmonic appeared in swept field only when the signal at third harmonic was registered also in the constant dc field. AC response at the third harmonic was observed only for Hc3>H0>Hc2 while signal at the second harmonic in a swept field was observed also below Hc2. AC response for H0>Hc2 can be ascribed to the surface superconducting states. Possible explanations of the experimental findings will be discussed