Surface resistance and penetration depth of YBa2Cu3O7−δ thin films on silicon at ultrahigh frequencies

The surface resistance Rs and the absolute value of the magnetic penetration depth λ of ultrathin YBa2Cu3O7−δ films on silicon are determined by THz-pulse transmission experiments. We find a minimal value of Rs for a film thickness of about 30 nm. The increase of Rs with film thickness above 30 nm reveals an increase of the density of weak links possibly associated with the formation of microfractures even below the critical film thickness of 50–70 nm.