Magnetic field orientation dependence of the microwave response in YBa2Cu3O7-d.

We present microwave resistivity measurements at 21 GHz in YBa2Cu3O7-δ thin film as a function of the temperature and the magnetic field. Measurements are taken in various relative orientations of the microwave current, dc magnetic field and c axis. Attention is focussed on measurements taken with the dc field parallel to the (a, b) planes. In moderate magnetic field, we show that the microwave magnetic response is made up of a vortex motion contribution, which can be described by conventional models, and a noticeable magnetic field induced increase of the quasiparticle density, which exhibits features typical of the existence of lines of nodes in the superconducting gap. We estimate the effective vortex viscosity for vortex motion across the (a, b) planes.