Generation of higher harmonics in superconducting YNi2B2C

We report the generation of higher harmonics when superconducting intermetallic YNi2B2C is exposed to an ac magnetic field Hac = H 0acsin (ωt) and a dc magnetic field Hdc. Application of an ac magnetic field (H 0ac>Hc1) leads to the generation of higher odd harmonics as is expected in conventional intermetallic superconductors. Interestingly, the application of Hdc in addition to Hac also causes the generation of even harmonics. This phenomenon is similar to that observed in high-Tc superconductors in which grain boundaries behave as Josephson weak links. We have studied the variation in amplitude of the higher harmonics as a function of H 0ac, ω, Hdc and temperature. The observed results are explained in terms of grain boundary weak links and a critical state model.