Strong reduction of field-dependent microwave surface resistance in YBa2Cu3O7−δ with submicrometric BaZrO3 inclusions

We observe a strong reduction of the field induced thin film surface resistance measured at high microwave frequency (ν=47.7GHz) in YBa2Cu3O7−δ thin films grown on SrTiO3 substrates, as a consequence of the introduction of submicrometric BaZrO3 particles. The field increase of the surface resistance is smaller by a factor of ∼3 in the film with BaZrO3 inclusions, while the zero-field properties are not much affected. Combining surface resistance and surface reactance data, we conclude (a) that BaZrO3 inclusions determine very deep and steep pinning wells and (b) that the pinning changes nature with respect to the pure film.