Microwave Harmonic Emission in MgB2 Superconductor: Comparison with   YBaCuO
  We report results of microwave second-harmonic generation in ceramic samples of MgB2, prepared by different methods. The SH signal has been investigated as a function of the temperature and the static magnetic field. The results are discussed in the framework of models reported in the literature. We show that the peculiarities of the SH signal are related to the specific properties of the sample. A comparison with the results obtained in ceramic and crystalline YBa(2)Cu(3)O(7) shows that the second-harmonic emission in MgB2 is weaker than that observed in ceramic YBa(2)Cu(3)O(7). 
A. Agliolo Gallitto, G. Bonsignore, E. Di Gennaro, G. Giunchi, M. Li   Vigni and P. Manfrinetti