Surface impedance of single crystals of high Tc cuprates as a function of magnetic field

In-plane penetration depth λab of Bi2Sr2CaCu2Oy was investigated at 45 MHz as a function of dc magnetic field H both in the Meissner state and in the mixed state. In the Meissner state, λab changes linearly with H. This is consistent with a recent theoretical prediction for d-wave superconductors. In the mixed state, it was found that the response is dominated by the pinning, except close to Tc. We extract the Labsch parameter as a function of the magnetic field, and found that it behaves H1.5 as was in conventional superconductors. This means that the pinning properties of the Bi cuprates are similar to that in conventional superconductors.