Absorption of electromagnetic radiation by superconducting yttrium barium copper oxide $(YBa_2Cu_3O_7)$: an oxygen-induced phenomenon

In the superconducting state, $YBa_2Cu_3O_7$ absorbs electromagnetic radiation over a wide range of frequencies (8 MHz-9 GHz). The absorption is extremely sensitive to temp., particle size, and the magnetic field and depends crucially on the presence of $O$. A possible explanation for the phenomenon based on Josephson-junction formation is suggeste