Superior microwave properties by post-annealing YBa2Cu3O7 thin films at low oxygen partial pressure

YBa2Cu3O7 (YBCO) thin films with improved properties have been recently reported by post-annealing in a low partial pressure of oxygen, similar to that used by in situ methods, compared to the usual post-annealing in 1 atm of oxygen. Here it is shown that the improvements extend to the microwave surface resistance. The surface resistance was measured at close to 10 GHz; the scaled value at 10 GHz and at 77 K is 240 μΩ. This value is as low as has been reported for YBCO thin films measured around 10 GHz made by any method, and is two orders of magnitude lower than the surface resistance of copper at the same temperature and frequency.